District 10 Como Community Council

Como Park Tree Trek - Sat. June 22 - 10am-Noon

The D10 Environment Committee hosts Tree Treks where community members can learn how to identify and appreciate the multitude of different tree species living in Como Park. Volunteer tree expert Stephanie Mirocha is our fabulous second-generation Tree Trek guide (her father was the original Tree Trek Guide). Upcoming Tree Trek events will be posted here (Sign up for our weekly newsletter to get Como Neighborhood news in your inbox).

This walking tour will be led by Minnesota Master Naturalist Stephanie Mirocha. She will provide fascinating facts, uses, and histories of many of the diverse tree species in the park. 

Dress for walking and the weather and meet between the Butterfly Parking Lot and the Labyrinth (adjacent to the Labyrinth – on the west side of Lexington Parkway near the pedestrian bridge).

Self-Guided Tree Identification Trek

In addition to the planned events each year, the Tree Trek program has also created and installed 42 Tree Tags on 39 species of trees around Como Park. 

The Environment Committee of the Como Community Council, as part of its educational activity, has organized a self-guided, pictorial tree identification program. Our intention is to introduce Como Park users to the variety of interesting tree flora in the park, some of which are quite unique. Understanding some of our tree species will lead to a greater appreciation of the botanical treasures found in the park. The location of each tree can be found on the Google Map (embedded below) or on the printable PDF map to the right.

The original Tree Trek was created in 2011 by committee member Chet Mirocha. A decade later (after Chet’s passing), his daughter Stephanie revived the Trek. The number of trees that are identified was doubled in 2021, and expanded again in 2022 and 2023.

Meet The Trees

This is a new section being added, species ending with x’s below are still being integrated into website, check back soon! 2/13/2024

American Basswood

Also known as: American linden, American lime, bee tree
Shape: oval with densely rounded crown, drooping lower branches
Leaves: broadly ovate, serrate, alternate
Flowers: cream colored in clusters, bisexual; monoecious
Fruit: nut-like drupe
Fall leaf color: pale yellow, tinges of brown or amber
Height: 80’ to over 100’

Newly emerging leaves in early May
Most flowering trees bloom during the spring season. Tilia is a summer-flowering tree, blooming from late June into July. The fragrance wafting from a basswood tree in flower is captivating to say the least, with scent notes as delicate as a fine wine. The flower parts of this species have a distinctive complexity that is similarly striking. Basswood’s floral bracts are a good example. After the leaves emerge in late spring, leaf-like floral bracts form into graceful curves out of the new leaf axils. The bracts are somewhat papery feeling, oblong shaped, and grow up to 5” in length remaining pale green throughout the growing season They’re quite attention-getting in the way their slender shape and light color waves in the breeze like ribbons, contrasting with the broad, deep green leaves growing alongside them. The bract exists to support each flower cluster’s main stalk which is fused along its lower half. The flower stalk then emerges from about the middle of the bract to hang freely as a naked stalk for a short length before branching into the flower cluster. The bracts can serve as wings aiding in seed dispersal later on after the nut-like drupes ripen. In fall, bracts turn brownish yellow, and can also persist on the tree along with some of the nutlets all winter.
 
Flowers and seeds
Bracts, scent, and the irresistible nectar-filled flowers blooming in profusion attract thousands of honeybee visits filling the tree with buzzing in midsummer. Bees so love these flowers that American basswood is also known as the ‘bee tree’. From the abundance offered within the creamy yellow petals, bees bring the flower scent notes back full circle in creating a wonderful honey as enticing as its flower source. 
 
Flowers grow in clusters, known in botany as ‘cymes’. The main stalk ends in a flower bud that opens first, followed by the side stalks below it with buds forming on the ends of their stalks for a total of 5 to 17 (or more) flowers per cyme. Basswood is monoecious, meaning both male and female flowers occur on the same tree, so each tree produces fruit. Basswood flowers are also bisexual having both male and female parts within each flower. An interesting difference here is that, unlike many monoecious trees typically relying on wind for pollination, basswood flowers are insect pollinated. The abundance of flowers produces many seeds; yet the main way American basswood reproduces is by sending out root suckers from the roots around its base. These form into young trees that establish themselves nicely alongside the main trunk into a little grouping that gets along quite well. 
 
Seeds in late July
Fruit is a nut-like drupe about ¼” across, green at first, then ripening to a grayish brown covered in very fine hairs. Chipmunks, mice, and squirrels love to eat the seeds, as do blue jays and thrushes. Indigenous traditional cuisine also utilizes the seeds by grinding them into a paste used for immediate consumption. 
 
All parts of American basswood are valuable, whether medicinally, for their edibility or for practical use. Basswood provides food for a variety of insect life in its role as leaf host for numerous species of butterflies and moths, including the eastern swallowtail butterfly and the red-spotted purple. The sap is high in sugar content for making syrup. Basswood leaves are full of nitrogen, calcium, magnesium, potassium (and some flavonoids) that remain in the leaves through fall, contributing to the richness of the forest floor beneath them. White-tailed deer prefer the leaves, twigs and buds of basswood. Humans can join in – at least in early spring – when the leaves are still tender and light green for a delicious and nutritious addition to spring salad mixes.
 
Seeds and bracts in October
American basswood bark is relatively thin skinned (which makes it sensitive to forest fires). The bark can be peeled off, soaked and separated to reveal inner fibers that are very strong. The Anishinaabe (and many other tribal nations) traditionally used basswood’s fibrous bark to make strong twine for weaving rush mats, and for sewing practical items together essential for everyday life. These could range from food storage bags and packets to sewing together sheets of birch bark to make a waterproof, tight covering for dome-shaped roofs of essential dwellings.
 
Basswood grouping
The tree’s common name, basswood, derives from the word ‘bast’, which is the fibrous part of a plant that comes from the thick phloem within the inner bark or stem. Historically, many newcomers from Europe arriving on the scene in the 1600s witnessed the many uses indigenous people were making of bast from the abundant Tilila trees surrounding them, and so dubbed this New World tree ‘bastwood’ for that important use, which morphed over time into the name, ‘basswood’. Some colonists were well aware of and had historically used bast from their own Tilia species in their native homelands across the seas – the Tilia trees they knew back home as ‘lime’ or ‘linden’. In Anishinaabe language, ‘bast’ is called wiigob, the same name for the basswood tree itself. The processed bast fiber is called asigobaan, indicative of the substantial use of this resource and therefore the need to name the important product made from it. 
 
Older trunks provide homes
Tilia leaves are heart shaped, no matter whether they are from Old or New World species. Basswood leaves dominate along the twigs in two rows in an alternate arrangement. Lower branches tend to hang downwards, presenting the simple leaves with their toothed edges. One way to tell Tilia americana apart from its close relative from Europe, little-leaf linden (Tilia cordata), is to compare the leaves, for a fair amount of little-leaf lindens have been planted throughout Como Park. Basswood leaves are quite large in comparison (3” to 10” long) while little-leaf linden leaves are no larger than about 3” in length and have 5-7 veins coming from the midrib (central stem). American basswood has 9 or more veins. (Interestingly, this less-veined comparison works for American beech vs. European beech as well, with the European version similarly having less side veins.) In addition to leaf comparison, the shape of the two species differs. Tilia cordata retains a tighter, more pyramidal form as it matures than its American cousin, and this is one reason little-leaf linden is more likely to be found lining the streets of urban and park landscapes. 
 
American Basswood leaf
FUN FACT: the “Father of Taxonomy”, Swedish botanist Carl Linnaeus, got his surname from his father who was required to take a permanent surname upon entering the University of Lund in the late 1600s. His father chose a Latinized version of ‘linden’, based on a huge, olds and beloved linden tree growing in the local area of his childhood.   
 
 

Winter Identification

  • Buds are smooth, rounded and reddish.
  • Buds have 1 or 2 visible scales, amber in color.
  • Buds grow alternately in a zig zag along the twig.
  • Current year twigs are brown, gray or reddish.
  • 5 to 10 bundle traces (vein scars).
  • False terminal bud sits at a 45 degree angle.
  • Young bark is greenish.
  • Mature bark is grayish brown with long, shallow furrows.

American Beech

Also known as: white beech, Carolina beech, beech
Shape: oval with rounded, spreading crown
Leaves: simple, coarsely toothed, alternate
Flowers: separate male and female flowers borne on same tree; monoecious
Fruit: 1 to 2 triangular nuts encased in a prickly husk (bur)
Fall leaf color: brilliant amber to golden bronze
Height: 60’ to 80’

Leaves are still intact in May

American beech is a crowning glory any season of the year. In fall, beech trees produce nutritious nuts that feed a variety of birds and mammals. In winter, the long, sharply tipped buds are quite apparent poking through the marcescent leaves. The buds point so far away from the winter twig they resemble thorns – an important distinction that aids well in identification. Throughout the winter, leaves remain on the branches in beautiful shades of reddish amber to light brown, holding on tightly until just before the new leaves emerge. Another distinctive trait of the beech tree is its pale gray bark, so smooth that it irresistibly beckons a hand to run along its surface.

Leaves are hairy at first

American beech is the only beech tree species that is native to North America. Minnesota is just west of the easternmost native range of American beech which stops in eastern Wisconsin. Its native range covers the mesic forests of eastern Wisconsin continuing eastward as far north as Nova Scotia and southern Ontario down to northern Florida and westward again to eastern Texas. It does not particularly like getting its feet wet and prefers habitats with well-drained soil. A beech tree takes its slow time in growing, reaching sexual maturity at about 40 to 60 years, with optimal seed production occurring at 80 to 100 years old. From there, life expectancy can reach 300 years or more. Beech trees are arguably well worth the wait, offering a treasure for many generations to come.

Singly toothed leaves

Leaves of the beech tree have singly toothed edges with each of the veins running parallel off the midrib ending in one of the sharp, widely spaced teeth running around the edges. American beech leaves are narrowly ovate, at first glance perhaps similar in shape to those of paper birch, but clearly distinguished from them by their singly toothed edges. Birch family species are doubly toothed. Ten to 14 pairs of veins run parallel off the midrib. The topside of the mature leaf is shiny, deep green, smooth, and waxy, showing a bit paler green below. Leaf margins are also slightly undulating, meaning they have a slight wave around the edges. An easy way to distinguish American beech from its European cousin, European beech, is to count the pairs of veins running off the midrib. European beech has only 5 to 9 pairs, much fewer than American beech.

Undulating leaf margins

In spring, the newly emerged leaves are hairy, both on the edges and flat surfaces. This is most likely a protective adaptation that buys the beech tree some time to gear up its energy before hosting the plethora of butterflies and other arriving insects its leaves will soon be feeding as smooth-surfaced adults. According to Doug Tallamy, author of Bringing Nature Home, American beech provides food for over 100 species of butterflies and moths.

Flowers are unisexual, occurring separately on the same tree, and develop as the leaves emerge. Male flowers are tiny and form in a roundish cluster on a 1” stalk. They rely on wind to pollinate the waiting female. Female flowers come in clusters of 2 to 4 on a shorter spike. The female flowers consist of leaf-like greenish bracts and tiny red styles. After fertilization, a fruit forms with a prickly husk, or ‘bur’, around it. The bur is green at first, then turns brown along with the ripening nuts inside.

Glorious American Beech

Fruit. In late summer, the burs (prickly husks) that formed around the ripening fruit split open to reveal 1 or 2 (rarely 3) triangular nuts. The prickles are not sharp like some other prickly husks can be, and you can easily rub them between your fingers. Empty burs sometimes stay on the tree all winter along with the leaves.

Edibility. Beech nuts are nutritious both for people as well as for their value in feeding and sustaining a significant variety of wildlife. They are high in protein — more than acorns have – as well as fats, carbohydrates and vitamins. Squirrels and chipmunks, raccoons, red fox, deer and porcupines just love these nuts. Black bears gear up as well to prepare for winter hibernation.

Birds that enjoy the nuts include blue jays, red-headed woodpeckers, nuthatches, and ground feeders such as wild turkeys and ruffed grouse. Hairy woodpecker and other insect foraging birds arrive to enjoy the plethora of insects (ants, leafhoppers, woolly beech aphid, and many moths and butterflies) that feed on the leaves. American beech also provides nesting habitat for cavity nesters like wood duck, and its strong branches provide good sites for hawks and other species.

Uses. While beech wood offers a hard and straight grain, it tends to take on moisture when exposed to outdoor air such as for furniture. For indoors, It’s very suitable and durable for furniture, flooring, chairs, desk and wood turning projects.

Winter Identification

  • Leaves remain on tree all winter (marcescent)
  • Buds are reddish brown and diverge widely from the twig, thorn-like.
  • Terminal buds are narrow, sharply pointed and about ¾” long.
  • Lower buds are the same shape but shorter.
  • Twig is dark purplish brown and zig zags between the buds.
  • Leaf scar is a semi-circle with indistinct vein scars
  • Bark is smooth, thin and pale gray or blue gray in color.
  • Trunk is short.

American Elm

Also known as: white elm, gray elm, water elm
Shape: vaselike with a spreading crown
Leaves: alternate, simple, doubly toothed, asymmetrical base
Flowers: bisexual, ” across, early spring; monoecious
Fruit: round, notched, single-seeded samara up to ½”, early summer
Fall leaf color: golden yellow
Height: 60’ to over 100’

Flowers newly opened

The streets, avenues and boulevards of many cities were once lined with the stately trunks of American elms one after another reaching their branches 60 to 100 feet or more into the air. Sweeping downwards, their upper branches arched toward those of a nearby elm, creating a shady, dappled canopy for every creature lucky enough to travel underneath. Beloved as ornamentals in urban landscapes, these graceful, vase-like tree shapes began to disappear starting in 1961 when Dutch elm disease (DED) began its devastation of all species of elm communities across their native range, roughly the eastern half of N. America. Large, mature elms still exist as survivors but are few and far between, especially in urban areas. If we have learned anything from this — and again more recently with emerald ash borer (EAB) — it is to avoid planting monocultures. Instead, many species of deciduous shade trees and evergreens now grace our streets, creating a beautiful new kind of urban landscape.

Female fuzzy styles and male anthers

American elm can tolerate the salty, droughty, soil-compacted, and air polluted conditions commonly found in cities. In its natural habitat, American elm prefers lowland hardwood forests along flood plains and swampy areas where ash and silver maple trees are frequent neighbors. Northern hardwood forests also offer good habitat for elms to grow alongside a variety of trees including basswood, sugar maple, yellow birch and red oak; again, the wetter areas are where American elm prospers.

Both male and female elm flowers are present on the same tree. This is termed ‘monoecious’ in botany, meaning ‘one home’. Further, in elm trees both male and female organs are present in the same flower, termed ‘bisexual’ (or ‘perfect’). In general, an American elm’s female stigma will not produce viable seed using pollen from its own tree’s anthers. How, then, does it avoid self-fertilization since each flower contains its own pollen? American elm flowers rely on the age-old trick of dichogamy where sexual parts ripen at different times within a flower. In this case, the species is protogynous, meaning the female parts mature before the male parts in each flower, reducing that flower’s chances of self-fertilization and increasing the flower’s chance of receiving pollen from other elms in the area. In April, the inconspicuous (⅛” across), petalless flowers open, creating a sort of hazy fringe of green and maroon filling the space around the still leafless twigs and branches. Thousands of elm flowers hang in drooping clusters of 3-5, the ripe female 2-part feathery style perfectly suited for catching pollen from anthers of nearby American elms to fertilize them. Flowers have no need for petals, nectar or scent to attract insects because wind is the key to elm tree pollination. April breezes sweep along elm limbs and transfer pollen tree-to-tree.

Mature flowers in early May

All that pollen, in addition, provides important nourishment for hungry honeybees whose winter food storage may be near depletion. If the temps are warm enough, any newly active bees may find forage in an elm (also maples and poplars) during a time of year when the early spring wildflowers have not yet opened. A month or so after pollination (about the time the leaves are fully grown), the delicious seeds ripen, serving up an abundance of food for the many small mammals and songbirds ready and waiting.

The fruit is a round, wafer-like seed called a ‘samara’ (winged seed) ripening into June. The samara is ⅜” to ½” across attached to one dry seed in the middle. American elm samaras have a distinctive notch or cleft at the tip forming two small lobes. A dense fringe of white hair all around the edges (margins) makes the samara rim fuzzy, but the flat surfaces remain hairless. The samara is light green at first, then dries to a tan color before it sails away, is eaten or both.

Seeds newly forming

American elm leaves serve as the larval host for several butterflies including the mourning cloak, question mark, painted lady and comma butterflies. The leaves are simple, taper to a sharp point at the tip, and are asymmetrical at their base. Edges are double-toothed, and the secondary veins go straight to them in parallel lines usually without forking. Leaves grow 3 to 6 inches long and up to 3.5 inches wide. They can have a somewhat rough surface texture as well — a feel I well remember as a child in our 1960s neighborhood when we used the leaves as money for playing ‘store’. At that time, American elms lined each block and a huge one graced our backyard. (For us, innocently, money really did grow on trees. American elms!)

Seeds maturing

Uses. American elm is a hardwood, but among the elms is considered a ‘soft elm’ (830 lbs. on the Janka hardness scale) compared to rock elm, which has very hard, dense wood (1320 lbs. Janka). All elm wood, however, is tough, with a particularly twisted, interlocking grain giving it both shock resistance and a superior ability to hold nails; this also makes its logs notoriously difficult to split for firewood. It warps easily on drying, and because of this works better for smaller objects like wooden utensils rather than for planing, shaping or turning. (Rock elm may work a bit better for this.) Once dried, elm wood takes very well to steam-bending, such as for the supportive parts of furniture, barrel staves and wooden trim used on old steamer trunks. Because it does not easily splinter, it was used in children’s wagons and sleds. In furniture making requiring joinery, the shock resistance of elm is useful, for example whacking a chair seat onto chair legs. Other uses include boxes, crates, pallets, and decorative paneling.

Mature leaf and seeds

Elm wood has many prized qualities, not the least of which is its remarkable water resistance when continuously submerged. Taking it in and out of water is another thing, for then it will rot easily. (Not so good for fence posts!) Historically, objects made of elm wood whose function were specifically to be subjected to conditions of constant water contact have lasted for centuries; objects such as canal gates, bridge pilings, keels of wooden ships, and ancient Rome’s underground water-piping systems are evidence of this. Ox yokes, harrows, handles, hinges on old Roman doors, and the wheel hubs of wagons or carriages were all good uses for this valuable resource. Even the stumps, tough just as they are, worked well as an anvil for blacksmithing.

Como Park’s tagged American elm is an exemplar of this grand species. Its bark shows the deep, interlacing furrows and flat-topped ridges of a mature elm. Its large diameter trunk holds its own next to widths that reportedly go well beyond 4 feet.

Winter Identification

  • False terminal bud sits at a 45 degree angle.
  • Leaf buds are reddish-brown, pointed.
  • Flower buds are larger and rounder than leaf buds.
  • Brownish twig slightly zigzags between buds.
  • Twig is slender, smooth in fall, hairy in spring.
  • Bark is light gray on younger trees, darker with age.
  • Mature bark has deep, interlocking furrows.
  • Bark pieces in cross section alternate in layers of light-brownish-light.

Amur Maple

Also known as: ginnala maple
Shape: single or multiple trunks with a broad crown
Leaves: opposite, 3-lobed with central lobe longest, margins toothed
Flowers: in clusters; either all male or bisexual; andromonoecious
Fruit: 2-winged samaras in clusters, red when mature
Fall leaf color: yellow to brilliant red, samaras often retained through winter
Height: 20’

Flowerbuds emerging in early May
Flowers clusters ready to open

In those heady years of early botany before the ecological harm of introducing exotics was understood, the intention for introducing Amur maple was its use as an ornamental as well as for its value in hedge and screen plantings. With a maximum height of only 20 feet, the latter purpose is particularly suited to Amur maple because the species is naturally a small tree. It is often referred to as a large shrub. The double samaras (winged seeds) are decoratively pretty in their clusters, turning red upon maturity contrasting against the green of the leaves. The samaras dry to a brownish tan, and many of them remain ornamentally on the tree throughout the winter.

Receptive female curly 2-part style

Native to China, Manchuria and Japan, Amur maple is named after the Amur river area of northern China from which the first specimens brought to the west were obtained. The Amur maple was introduced into N. America in the 1860s and has become increasingly invasive in the northeast and midwestern states ever since. In MN, the U.S. Dept of Ag. labels it a Specially Regulated Noxious Weed. What makes Amur maple so invasive is that it easily reproduces by seed and its decorative clusters produce a lot of seed to release into the wind. Amur maple easily naturalizes in open wooded areas, disturbed areas (such as clear cuts), and grasslands. In all cases, it alters the native habitat it establishes itself in, displacing native shrubs and understory trees, or shading out native flowers and grasses. Like other maple species, Amur maple sprouts very easily from the cut stump. The species is cold hardy to Zone 3.

Seeds newly forming, early June

Leaves are 3-lobed with doubly toothed margins. The main lobe is significantly larger and longer than the two side lobes.

Flowers. Amur maple usually blooms by mid-May. Pollination is achieved by insects and wind. The flowers begin to form after the new leaves have unfurled, and bloom at last when the leaves are mature. Flowers are fragrant and white, borne upright in small panicles about 1½” long. Each individual flower is about ⅛” across, and either all male (unisexual) with only stamens, or bisexual with both stamens and styles – a botany structure that defines this species as andromonoecious. This sexual system is very rare in plants and lends an interesting aspect to Amur maple’s story.

Seeds and leaves early September

Samaras hang in clusters, their double-winged seeds forming a very small angle between them so that the widest part of the drooping wings almost touch each other. Samaras are winged achenes – dry, one-seeded fruits that do not split open to release the seed when ripe. That’s where samara wings come in handy, to help the seed disperse as far as possible while spiraling down on a windy day.

Wildlife. Amur maple samaras are eaten by forest creatures including squirrels who seem to love all maple seeds! Deer and rabbits use the leaves as browse, and the branches provide good cover for nesting sites.

Winter Identification

  • Buds are opposite along the twig.
  • Buds are small and blunt, reddish brown or paler.
  • Seed cluster comes right out of the terminal twig end.
  • Seeds often hold on into winter.
  • Twig is reddish brown and smooth .
  • Leaf scars are U shaped.
  • Bark is smooth and gray when young.
  • Mature bark is grayish brown and shallowly fissured.

Austrian Pine

Also known as: black pine, European black pine
Shape: pyramidal when young; majestic, broadly spreading, full crowns at maturity
Leaves: dark green needles 3” to 6” long in bundles of 2
Strobili: males orangish yellow; females reddish to purple; monoecious
Seeds: winged seeds on scales of egg-shaped, woody cone in 2nd year
Fall leaf color: evergreen; needles persist 4 to 7 years
Height: 40’ to 60’ in cultivation; to 100’ in native forest habitats

side view of branch bud

Austrian pine is native to Europe but is much more widespread than its common name implies. In Latin, nigra means black, referring to the dark color of the bark. In Europe, Austrian pine is also generally known as black pine or European black pine. Its broad range covers the area of the Mediterranean extending in a wide swath from Portugal and southern Spain across to Turkey, the Balkans, to the Crimea, with outliers in the mountains of northwest Africa. It also grows on the islands of Sicily, Corsica and Cyprus. Taxonomists identify a number of varieties and subspecies of Pinus nigra. The most common seed sources originally brought to the U.S. came from trees growing in Austria and the Balkans and these did very well here. Black pine thus began to be referred to as Austrian pine in the U.S., first introduced and cultivated in 1759 both for its hardiness in shelterbelts and windbreaks as well as for its beauty. This species does best in deep, well-drained soils with plenty of moisture.

Branch bud with 1st year cones

Red pine and Austrian pine needles closely resemble each other. Both species have needle-like leaves that occur in bundles of two attached to the twig on a peg-like structure. Closer comparison will show Austrian pine needles are darker green, thicker, stiffer, and often have a slight twist. One test is to bend the needle in half. Red pine needles will snap in two every time. Austrian pine needles are much more flexible and usually do not break. Austrian pine branch buds in winter are about the same shape and size as red pine buds. These are pointed, around ½” to ¾” long with reddish brown, loose bud scales with whitish, papery margins. The difference here is that Austrian pine branch buds are a bit stickier with resin. Austrian pine seed cones are larger on average than red pine seed cones and, unlike red pine, have tiny prickles on the tips of their scales, especially on 1st year cones. 2nd year Austrian cones may still retain a few prickles, but typically they are deciduous.

Pollen cones

Reproduction. Austrian pine is a conifer (cone-bearing tree) classified in the group of seed-bearing plants called ‘gymnosperms’. These are ancient plants that arose and evolved from the seed fern group starting around 390 million years ago. Gymnosperms are defined as plants that reproduce by means of an exposed ovule (translating as ‘naked seed’ in Greek). Unlike the other seed producing group, angiosperms (angio = vessel), gymnosperms do not form fruit as they have neither an ovary to protect their seed nor any flowers. Instead, they have strobili (see below). Fossils of cone-bearing gymnosperms have been found dating back to over 300 million years ago — millions of years before flower-bearing trees first appeared.

Strobili are the reproductive structures of gymnosperms (singular, ‘strobilus’), a formal botanical term for what are commonly called ‘cones’. Borrowed from the ancient Greek, strobilos, meaning spiral or whirling, the term refers to what overlapping scales do structurally on male and female strobili. These can be attractively colored in spring, as are many in the Pine family in the early stage of sexual development – well worth observing during that time of year.

Seed cone forming in early June

Both male and female strobili are located on the same tree, making the tree monoecious, meaning ‘one home’. How do monoecious trees prevent self-pollination? One way conifers do this has to do with gravity, as most seed cones reside toward the top of the canopy with pollen cones forming lower. The idea is that not all the wind dispersing pollen grains will find their way straight upwards, making them less likely to fertilize their own tree’s seed cones, just some of them as the pollen wafts onto females of surrounding area trees.

In spring, Austrian pine male strobili (pollen cones) are orangish yellow in color, formed in symmetrical clusters at the base of new branchlets. Each strobilus is about ½” to ¾” long, consisting of overlapping bracts (microsporophylls) spiraling around a central axis. These scale-like modified leaves carry pollen-producing microsporangia, or pollen sacs, on their lower surfaces. When ripe, the pollen sheds into the wind. After the period of pollen release, male strobili dry up and deteriorate.

Branchlet and unopened seed cone

In springtime, new branchlet growth extends upwards and is much lighter in color than the previous year’s foliage, making the newly forming pine branchlets stand out in light green formations named for what they resemble – candles. I love this term! Austrian pine’s female strobili (seed cones) are reddish to purple in early spring, and form at or near the tips of new candles. Each female strobilus is small, egg-shaped, and consists of bracts (megasporophylls) spiraling around a central axis. These scale-like, modified leaves hold the structures upon which the megasporangia, or ovules, lie open to the air. Ovules are simply undeveloped seeds, waiting for pollen spores to land on them so that they can draw the right one inside and begin the long process toward fertilization that results in a fully ripened seed.

Seed cones of Austrian pine (like other species in the Pinus genus) take 2 years to mature. At the end of the first year, the developing Austrian pine seed cone is only about ½” long and is armed with a spiny prickle on each scale tip (umbo). The umbo is the first year’s growth of the scale, showing up as a protuberance on the 2nd year cone’s scale tips. This can be smooth, as in red pines and Scots pines, or quite sharp as in Austrian pines and ponderosa. The umbo of a mature Austrian pine can still retain the tiny prickle from that first year’s growth, but typically at maturity it will fall off. At the end of the Austrian pinecone’s 2nd year, two winged seeds on the top surface of the seed cone’s scales have ripened, ready to fly away on the wind. Not all seeds exit the cone right away. Mature Austrian pinecones range from 2½” to 3” long. After shedding seed, the cone usually falls from the tree, but it can also remain attached for several years.

Mature seed cone

Uses. Besides its use in shelterbelt plantings and as an ornamental, Austrian pine is often used in urban landscaping because of its high tolerance for urban pollution — possibly the most tolerant of the pines. It is also a species that has been used in land reclamation, such as after strip mining. Austrian pine wood can be used for timber as well, perhaps used more this way in Europe than in the U.S., where it is used more as an ornamental or as a shelterbelt tree.

FUN FACT: Austrian pine was one of several species of trees — over 220 million trees in all — that the CCC and WPA planted totaling 18,000 linear miles of windbreaks during the Great Dust Bowl era as part of Roosevelt’s New Deal project. Starting in 1934 and lasting 8 years, the Great Wall of Trees shelterbelt project extended from N. Dakota to Texas. Many of these shelterbelts remain intact today or as remnants in need of restoration.

Winter Identification

  • Branch buds are ½” to ¾” long, pointed, and sticky with resin.
  • Buds scales are reddish with papery margins.
  • Leaves occur in bundles of 2 and are dark green.
  • Needles are stiff, but also flexible when bent.
  • Bare twigs are orangish brown, rough with peg-like structures.
  • First year cones are present with small spines or prickles (umbos).
  • Mature bark has dark gray to black irregular plates, more furrowed with age.

Balsam Fir

Also known as: balsam, Canadian balsam
Shape: pyramidal to conical with a spire-like crown
Leaves: flat needles, white banded on underside, ⅜” to 1” long
Strobili: male initially red; females reddish tinged to purplish; monoecious
Seeds: winged, resinous ⅛” to ¼” long on fan-shaped scale in upright cone.
Fall leaf color: evergreen
Height: 40’ to 80’

Hiking in central and northern Minnesota, you will most likely encounter a variety of evergreen species along the trail interspersed with such deciduous trees as paper birch, maple, oak and aspen. Look for some tall, very narrow evergreens in particular that may be pointing their top branches skyward like a narrow spire. Let’s take a look at the leaves and some other traits of your tree to determine whether this is a balsam fir.

Needle attachment and underside

Leaves. If you can reach them, feel how soft the needles are as they grow out at all angles from the twig like a bottle brush. They are singly borne, dark green, and ½” to 1” long. The twig you are holding will most likely show how the needles can arrange themselves each to receive the most amount of light as they grow in two horizontal, parallel rows along the twig. Needles growing in areas of the tree farther up the crown that receive more sunlight will not spread out like this and will instead simply spiral around the twig. Roll one of the needles between your fingers, and you’ll find that you’re unable to. Because the needle surface is flat, it will be more like a popping back and forth motion.

Turn the twig over to find the many whitish dots of stomata (the leaves’ breathing pores) that run in two bands on either side of the dark green midrib that stripes the middle of each leaf. Each leaf attaches itself directly onto the twig like a cup or foot, with no peg or stem-like structure holding it up. When a branch dies, the twig remains smooth to the touch, without the peg-like bases found on spruce trees. Needles may either be straight or have a slight curve at their ends. Individual needles of balsam fir last from 8 to 13 years on the tree.

Balsam fir bark is gray, smooth and blistery with aromatic resin that may be oozing a fresh or dried line of pitch running down the length of the trunk. On younger trees, the bark is smooth grayish brown to greenish and covered with thin blisters you can actually pop. These blisters contain a stickery, aromatic resin. Older trees have more of a rough surface with less blisters. Many horizontal lines mark the bark along the trunk.

If things are matching up here, chances are good you are meeting the beautiful balsam fir of the north woods, inviting you to stay a while for some quiet time beneath its scent-filled boughs. Let its gentle presence flow through you.

Balsam fir, like many evergreens, is native to cool climates and can grow in many soil types, preferring moisture over dry soils. A cold-loving tree, balsam fir evolved alongside black spruce, paper birch, quaking aspen and white spruce in their northerly, Canadian boreal forest range. In Minnesota, balsam fir grows in mixed forests that additionally may include northern white cedar, maple and oak.

Balsam fir is a conifer in the Pine family along with the pines, spruces and other firs. While these all share many traits (for example needle-shaped leaves that are evergreen), there are some important differences that separate true firs (Abies) from true pines (Pinus) and true spruces (Picea). The upright growth of seed cones is a big identifier. From pollination through maturity, fir seed cones remain pointed upwards, continuing to retain on their branch as the cone degrades into fragments and the seeds fall off. By autumn, all that remains is the central stalk, whether the seeds have dispersed into the wind to be eaten by some ground feeding birds and mammals, or whether some hungry squirrel or other creature has consumed the seeds up on the branch right on the spot.

New leaf growth

Reproductive buds form in the first year but are very tiny. In the spring of the next year, these develop into the male and female strobili. Strobili are reproductive structures (singular, ‘strobilus’) of gymnosperms, the formal, botanical term for what are commonly called ‘cones’. Borrowed from the ancient Greek, strobilos, meaning spiral or whirling, the term refers to what overlapping scales do structurally on male and female strobili. Both male and female strobili of balsam fir are located on the same tree (monoecious, meaning ‘one home’). However, they reside in separate areas of the tree.

Male strobili (pollen cones) are less than 1” long and form in clusters underneath last year’s twigs. They are located lower than the females, towards the middle of the crown and are small but power-packed, maturing mid-May into June and releasing an abundance of pollen into the wind to land on the waiting females. After the period of pollen release, male strobili dry up and deteriorate.

Female strobili (seed cones) are purplish and about 1” long before fertilization, located in the uppermost part of the crown. They also form on last year’s twigs but are located on the upper side of the twig.

Like all gymnosperms, balsam fir ovules are naked to the air as they await pollination, not enclosed in an ovary like flowering trees (angiosperms). The ovules of many gymnosperms form a pollination drop to help them capture pollen coming from male cones, but species in the Abies genus do not do this. Firs rely on rainwater and gravity to capture pollen, perhaps another reason for their upright orientation. Pinus and Picea (the pines and the spruces) do secrete pollination drops, so here again is another difference.

Because the seed cones are located in the uppermost part of the tree and they never fall off, you likely won’t readily see them up close. The seed cones mature and ripen in the autumn of the same year as pollination and are about 2” to 3” long at maturity. The mature cones are purplish to dark brown with fan-shaped scales that stay very tight and flat to the surface until the ripened seeds start to shed from the base of the cone upwards. Like many parts of balsam fir, the seed cones are also very resinous, often coated with that sticky, fragrant, liquid.

Seed cone central axis in October (Photo by Jennifer Victor-Larsen)

Balsam fir has a shallow root system making it susceptible to big windstorms that can uproot them, especially in below freezing temperatures. The thin, resinous bark is also easily ignitable making balsam fir extremely intolerant of fire. On the plus side, balsam fir as a species is very shade tolerant, and can replace itself. This only works if, over time, another tree falls and opens up a space to let in more light, which is quite likely to happen somewhere in the vicinity of the young balsams. The strategy here is that before this happens, a whole bank of balsam fir seedlings – thriving but staying rather small — are at the ready, being already of a good size to take advantage of the newly opened space so that one or more of them can grow to maturity.

Pests that plague balsam fir include the eastern spruce budworm, a native insect that was noticed appearing regularly in Minnesota beginning in the 1950s.

Wildlife. The edibility of balsam fir needles for helping wildlife get through winter is attested to by the steel wire cage I must place around vulnerable young trees I’ve planted, to protect them from being eaten down by mammals such as moose and white-tailed deer. Balsam fir needles may not be the most digestible food around and thus play a lesser dietary role, but by the time the preferred foliage of aspen, birch and willow become scarce in late winter, many forest creatures rely on balsam fir (and other evergreens such as spruce) to get them through. Grouse, both ruffed and spruce grouse, are happy to eat the needles of balsam fir. White-tailed deer do as well if there is nothing else around. Cottontails and snowshoe hares join in, as do moose – all relying strongly on balsam fir, especially in late winter. As for the aromatic bark of balsam fir, well, that seems quite yummy for porcupines to gnaw on!

The seeds of balsam fir feed many, including red squirrels and chipmunks. Birds that also love the seeds include ruffed and spruce grouse (again!), chickadees, red-crossbills, pine and evening grosbeaks, jays and nuthatches. The songbirds visiting just feed on the seeds right from the cone on the tree. The yellow bellied sapsucker behaves true to its name, not only for the sap of maples in the spring, but also for the nourishment found not far into the resinous bark of balsam fir. With all this activity attracting wildlife to balsam fir trees, it should come as no surprise at how often various mammals use the thick foliage for cover, nesting sites, and especially roosting sites for grouse.

Uses. Balsam fir is one of the most popular Christmas trees. This species does not readily shed needles like some of the others. My childhood family was one of those who preferred balsam fir, and I can recall my dad bringing one in each year for our Christmas tree. All parts of the tree contain various kinds of helpful bioactive compounds useful in medicine, worth exploring. Many other traditional uses for balsam fir’s sticky resin existed before synthetic glues replaced them. Wreaths and other decorations, incense, and balsam fir pillows are a few examples of ways balsam fir is used in the craft industry. Balsam fir wood is also useful for pulp, light frame construction, paneling, crates, plywood, barrels and crates.

Winter Identification

  • Buds are covered in clear, sticky resin.
  • Twigs are mostly opposite and tan with shortish hairs.
  • Needles on lower branches form in two rows, flat on branch.
  • Needle underside is lighter than the top.
  • Leaf scars are circular and flat, no pegs or bumps on the twig.
  • Young bark is smooth, pale gray to greenish, covered with resin blisters.
  • Mature bark is rougher with fewer blisters showing.

Bigtooth Aspen

Also known as: poplar, large-tooth aspen, “popple”
Shape: tall and slender with a narrow crown and short branches
Leaves: simple; alternate; margins have large, blunt teeth; petioles are flat
Flowers: male or female catkins on separate trees; dioecious
Seeds: 2-valved ovoid capsule, shedding May into June
Fall leaf color: Brilliant yellow tinged with orange and red
Height: 40’ – 60’ in Minnesota, rarely up to 95’

Male catkin

You may have noticed how the leaves of certain trees continually shimmer and flutter all summer long, catching your eye with their constant movement. These are the aspens, sending out a greeting to everything around them, and usually bringing a smile from me. Minnesota is home to a magnificent number of aspen trees, adding beauty and important wildlife habitat to the landscape as well as timber for practical uses in our everyday lives. Aspen holds a tremendously valuable place in the forest ecosystem as a keystone species, promoting biodiversity and sequestering carbon — just two among many important roles aspen holds. Two related species native to Minnesota are commonly found across the state, bigtooth aspen and quaking aspen (Populus tremuloides). A comparably short-lived tree, individuals live around 100 years while groves taken as a whole deteriorate somewhat before that.

Leaves. Try rolling an aspen leaf stalk between your fingers and you’ll find that a smooth roll won’t happen, more like a popping motion from side to side. This is due to the physical structure of the leaf stalk (or petiole). The entire petiole is flat. At the point where it emerges from the leaf base, the stalk is at right angles to the leaf, then twists slightly the rest of the way to the twig. This little flat sail is what catches the wind to make aspen leaves flutter and rustle at the slightest puff of breeze. In autumn, bigtooth continues its decorative show by turning a brilliant yellow to deep orange with tinges of red (depending on the year) shining colorfully against the deep blue of the autumn sky. Leaves are rounded or slightly heart shaped at the base of the blade, not straight across like a cottonwood leaf base. The underside of a bigtooth aspen leaf is paler than its top.

Pollen catkin closeup

Compared with quaking aspen, bigtooth aspen leaves are more broadly egg-shaped, but the biggest difference between them is found in comparing the “teeth” around their edges. Quaking aspen leaf edges are finely serrated, while bigtooth aspen leaves have very large blunt teeth just like the name implies. “My what big teeth you have!” definitely applies here! Bigtooth aspen trees also achieve greater size than quaking aspen, potentially growing a trunk diameter up to 30”. Leaves emerge after the tree’s flowers have finished pollinating and are forming fruit. When they first unfold, bigtooth leaves are covered on both sides with fine, white woolly hair. The twigs are also covered in this way. This is quite similar to another one of the tagged trees in the park, the nonnative white poplar (Populus alba). The difference here is that white poplar never loses its “underfur” of white woolly hair on the leaf underside, and which gives white poplar such a dramatic and decorative effect. Bigtooth aspen, on the other hand, outgrows that furry stage so that by the time the leaf is fully matured the white fuzz is no longer intact and has completely disappeared.

Female flowering look for red styles

Bark. Because of their thin, light colored bark, aspens are sometimes mistaken for paper birch, especially quaking aspen with its very light, smooth bark. Paper birch, however, has a chalky-textured, peely bark. Aspens have neither. Instead aspen bark hugs the tree smoothly and tightly, not at all like the peely, white bark of paper birch. Now let’s look closer at bigtooth aspen bark in comparison with its cousin, quaking aspen. Bigtooth aspen has the darkest bark, greenish gray to nearly olive all the way up. Quaking aspen bark, in contrast, is a much lighter greenish gray to nearly white colored (again where the confusion with paper birch arises). If still in doubt, look at those leaves again! Dark, diamond-shaped lenticels (pores), scaly ridges and other patterns form on aspens over time. Soon, identifying the markings on the various trees will become like second nature and you will easily know the difference between all three of these species.

Interestingly, unlike the bark of most other deciduous trees, aspens keep photosynthesizing all winter long even after they have lost their leaves. They can do this because their inner bark contains chlorophyll, just like leaves do, allowing them to keep making sugar for food energy to help them get through the cold months. Perhaps that freshness is why gnawing mammals love this nutritious snack!

Seed catkin developing in May

Flowers and seeds. Male and female flowers are on separate trees (dioecious, from Latin meaning ‘two homes’) in hanging clusters called catkins. Flowering happens early on in the season before the leaves emerge. Bigtooth does their flowering 2 to 3 weeks after quaking aspen’s pollination is completed – another difference between the two species. Male bigtooth catkins are 1” to 3½” long with tiers of red stamens. Female catkins are 1¼” to 3” long, but during fruiting time can grow to almost 6” long. Each female flower has a 2-chambered ovary with a pair of split stigmata on the tip of the pistil. After pollination, a ¼” long, 2-chambered capsule forms, splitting open when ripe. Inside each capsule are many tiny seeds, each with a long silky tuft of hair attached to one end. Each catkin contains between 70 and 100 seeds. It takes about 4 weeks after pollination for the seeds to ripen. Then, during May into early summer these seeds with their fluffy tufts ride on the wind and disperse.

While seeds surely germinate given the right conditions, the main way aspens regenerate is through root suckering. An individual aspen tree of either species will send out root suckers that in turn send out another and, in this way, clone themselves as they colonize an area. Quaking aspen clonal colonies can be quite large and tend to be larger in general than those of bigtooth aspen. Bigtooth aspen has a widespread system of side roots with descending sinker roots that go fairly deep, much deeper than quaking aspen. Though they often grow in the same area and habitat, the deeper root system of bigtooth tends to make this species thrive in drier, upland forests along with paper birch, maples, basswood and oak. Quaking aspen grows as a neighbor as well, but overall does better than bigtooth in areas with wetter soils or frequent flooding which bigtooth just can’t take. Bigtooth aspen is also a bit more shade tolerant than quaking aspen, one reason you will often find bigtooth either scattered or in small groves in mixed forest settings. Their sucker spreading then pauses against the shade of longer-lived climax trees nearby.

Wildlife. An area supporting aspen trees in different stages of growth is one the most important habitat requirements for ruffed grouse for breeding and raising young, including eating the leaves in summer and finding good forage during winter on the mature trees’ male catkins, twigs and buds. White-tailed deer and moose join in, browsing also on the young shoots and leaves in summer as well. Older bigtooth aspen trunks tend to develop holes and crevices that provide shelter for cavity nesting birds like owls and woodpeckers and nice den sites for small mammals like red squirrels.

Beavers are more likely to encounter the moisture-loving quaking aspen alongside shores, but they love the inner bark, leaves, twigs and branches of any aspen they encounter as one of their preferred food sources. Why stop there? They fell the trees and take the branches of aspen back to their home site to use as lodge timbers and to store for winter food. Beavers aren’t the only gnawing animals in the forest who find great nourishment in the bark of aspen. It’s one of porcupine’s favorites along with hares, cottontail rabbits and meadow voles.

Glorious bigtooth

Aspens are in the Willow family, a family that includes willows, aspens and cottonwood. The Willow family is second only to the oaks in their important role of providing support for hundreds of species of insects (including moths and butterflies). As is the story of the web of life supporting each other and evolving together, the many insects that rely on aspen end up also attracting numerous species of songbirds who eat them. The viceroy butterfly is an example of a specialist whose caterpillars rely specifically on the leaves of aspens and willows for their life cycle. So, hooray for aspens, giving us this beautiful orange and black butterfly resembling a smaller version of a monarch! And the web of life story continues from there with so many other species of insects, mammals and birds this tree nourishes.

Fall color

Uses. Aspen wood is straight grained and soft. The timber’s main use is in providing pulpwood for paper making. Other uses include production of particle board, structural panels, pallets, boxes, matches and chopsticks.

Winter Identification

  • Buds are alternate, pointed, and reddish brown beneath white wooly hair.
  • Buds are ¼” to ⅜” long and are not sticky or gummy.
  • Twigs (new growth) are reddish brown with no noticeable lenticels.
  • Leaf scars are heart shaped and knobby, like “steps” up the twig.
  • In cross section, the pith of twigs show a 5-pointed star.
  • Young bark is green or yellowish gray, thin, smooth with scaly dark markings.
  • Mature bark is dark brown, thicker with flattened ridges and narrow furrows.

Black Locust

Also known as: false acacia
Shape: crown irregular
Leaves: alternate, compound pinnate
Flowers: white, late May in fragrant, drooping
clusters, unisexual; monoecious
Fruit: up to 10 hard seeds (<⅛ long) in a thin, flat pod 2” to 4” long maturing to brown
Fall leaf color: golden yellow
Height: 40’ to 60’ in Minnesota

Flowers

Black locust is not native to Minnesota. This tree’s range covers the eastern U.S. from Pennsylvania to the Ozarks and lower slopes of the Appalachians. That said, it is now quite widespread across the world, introduced into Europe in the 1700s for its fragrant flowers that produce pollen bees use to make a much sought after honey, a prized product called ‘acacia honey’. Black locust was also introduced across the U.S. because of its rot resistant wood for mine timbers and other outdoor uses. The species grows well outside its native range, and in many places (including Minnesota) is considered invasive as it has naturalized into the landscape. The problem is that black locust can become quickly established, escaping and reproducing by seed and then when established, spreading rapidly by root suckers that crowd out native shade trees.

Flower closeup

Historically, black locust wood in its native range along the east coast was highly valued. Many would even say unequivocally that this is one of the trees that built our nation. Because of the extreme hardness and rot resistance of the wood, for example, the first builders of Jamestown used black locust for corner posts when constructing the first buildings in that historic city. Those buildings and their four supportive black locust posts are still standing. A tough tree, black locust was planted for windbreaks as well as for its nitrogen-fixing qualities, both of which were just what early settlers were looking for in a tree as they began establishing new farms. The tradition continued, as Americans in the war of 1812 used black locust in shipbuilding, shaping the rot resistant wood into fastener pegs. The resulting ships were superior to British fleets using less strong white oak for pegs. The wood was valuable beyond the east coast for use as mine timbers and railroad ties. Today, many of those same tough qualities are valued and used, for example, in planting black locust trees for land reclamation in abandoned mine sites. Due to the rot resistant nature of black locust wood, other uses include fence posts and outdoor furniture, for example, which usually can last for decades. Black locust’s very hard wood gives it high heat output for burning in wood stoves, as the wood is very slow burning and efficient.

Compound pinnate leaf

Leaves are singly compound pinnate, meaning that each leaf consists of a central rachis (stalk) with several pairs of leaflets along it. Each leaf has about 7 to 9 pairs of leaflet pairs going up its rachis, including a terminal leaflet at the tip. That’s it, no extra compound leaves. Leaflets are elliptic to narrowly egg-shaped, rounded at the tip, and up to 2¼” long. In comparison with honey locust’s doubly pinnate leaves, black locust leaves are larger and can be distinguished by the terminal leaflet – something honey locust typically lacks.

Ripened seed pod

Edibility and toxicity. All parts of the black locust are inedible and toxic, except for the flowers, The flowers can absolutely be eaten when fresh. Pick them while they are still young and succulent. They are delicious and possess their own subtle taste along with their own, particular, beautiful fragrance.

Flowers appear in late spring and are insect pollinated as they cascade their showy, 5 petaled butterfly-like fragrant blossoms down in pendant racemes — a flower cluster where each flower is attached to a central stem by a short stalk. Black locust is in the Pea family, and the flowers with their upper and lower petals and tubular shape reflect this. Consistent with Pea family members, the flowers form seeds inside pods after pollination.

Seed pods persisting in winter

Seed pods have up to 10 mottled seeds inside a tan to dark brown pod which (along with the bark) contains the toxic glycoprotein, robinin, a lectin that is similar in toxicity to ricin (which is found in castor beans). The pods grow up to 4” long pods, much shorter than honey locust pods, and without the twisting curl of honey locust pods. Thorns, if there are any, are only about ¾” long coming from the leaf scars, and usually fall off older twigs.

Pests include the black locust borer and the locust leaf miner which attack the tree, but do not usually kill it.

Winter Identification

  • A cluster of 3 to 4 buds are embedded in old leaf scars under twig bark.
  • Buds, in other words, are Invisible or hidden.
  • Terminal buds are absent.
  • Leaf scars may have a pair of short spines.
  • Seed pods typically stay on the tree through winter.
  • Younger bark is smooth and gray or brown
  • Mature bark is coarse and deeply furrowed with forking ridges.

Black Walnut

Also known as: American walnut, eastern black walnut
Shape: large and tall with open, broadly spreading crown
Leaves: alternate, pinnately compound, usually no terminal leaflet
Flowers: monoecious; male catkins and female flowers on the same tree
Fruit: nut inside a greenish husk; fruit is round and 1½” to 3” in diameter
Fall leaf color: golden yellow, amber or reddish orange 
Height: 50’ – 80’, can reach 100’ or more with up to 3’ diameter trunk

Black walnut is a highly prized hardwood valued for making furniture, veneer, flooring, oars, gunstocks, musical instruments, and for wood carving and turning. Once it’s cured, the wood is very stable, just one of its many assets. It is also a beautiful tree that produces delicious, edible nuts. The husks are used in traditional dyes for basketry and fiber work to create colors in rich, dark brown tones. Black walnut also has a rich medicinal tradition that continues into modern usage.

Male catkins emerging early May

Edibility. Black walnut is not the same as the English walnut (Juglans regia) that you find in grocery stores. Black walnut is our wild, native N. American tree producing nuts with a richer, bolder and more distinctive flavor in comparison. Black walnuts also have higher protein content than English walnuts, and in fact contain more protein than any other tree nut at 21%, comparable to protein amounts found in meat. Black walnuts are very high in fat as well, 59%, (low in saturated fat, high in unsaturated including omega-3) with low carbs and a good amount of vitamins, iron, several minerals and some fiber thrown in for good measure. They are not easy to process, however, because the shells are very hard; still, foraging peoples have done so for millennia for good reason. One interesting variation, a tradition from The Haudenosaunee Confederacy (east coast nations), is to boil black walnut nut meats to make a refreshing beverage.

The fruit is a nut encased in a hard, bony, textured shell surrounded by an up to 3” diameter, greenish husk. The husks are thick, leathery, and not sticky. They exude a pungent, citrusy odor (as do the leaves). For foragers, the nuts can be collected after they fall from the tree (before the squirrels get them) and before they look even slightly moldy. The big thing to keep in mind about the husk – as you may have found out inadvertently already — is that scraping it open without gloves will stain your skin for at least a week and there will be nothing you can do about it! The next step is the challenging task of removing the nuts from the shell (many ways have been devised), but the delicious reward is well worth the effort.

Female fruits early June

The chemical compound, juglone, is what causes that deep staining, and is present in a neutral, nontoxic form called ‘hydrojuglone’ in almost all parts of the tree except for the nut meats themselves. Buds, husks and roots have the highest amounts, followed to a lesser degree by the leaves and stems. When exposed to soil and air, hydrojuglone oxidizes into juglone which is then introduced into the soil when these parts break down over time. Juglone inhibits some species of plants’ abilities to grow and thrive beneath the dripline of the canopy (and even extends further) while other species are not affected at all. Gardeners might want to confirm there’s no black walnut tree in the yard next door because some veggies (i.e. tomato, rhubarb, cabbage, eggplant, potatoes, peppers) are juglone intolerant. Other veggies (i.e. snap bean, beet, melon, carrot, corn, and squash) are unaffected. My own woodland garden with its young black walnut tree enjoys false Solomon’s seal, white avens and spirea growing directly beneath, with wild ginger, Jack in the pulpit, Joe Pye weed, and bleeding heart all (so far!) growing nearby just fine.

Leaves

These types of compounds that can affect the growth of nearby plants are referred to as ‘allelopathic’. They discourage nearby competitor species from getting too close. Black walnut, with its high amounts of juglone (more even than others in its genus) is famous for this behavior. However, many species produce allelopathic compounds that give their survival an edge. These are roughly divided into two categories, the phenolic compounds (such as juglone and tannin) and the terpenoids. What helps plants also helps us, as these compounds have antioxidants and other helpful effects that we crave and love. For example, the bitter taste of tannins in coffee and tea is more than offset by the caffeine and antioxidant properties they also offer; the pleasant scent we so love emanating from evergreens comes from terpenoids.

Leaves are pinnately compound, 8” up to 2 feet long with up to 19 leaflets. There may be a smaller, less developed terminal leaflet, or it may be absent altogether. The leaf stalk is covered in sticky hairs. Leaflets are finely toothed, and leaves are often crowded at the branch tips. Tops are mostly smooth while the underside is soft and downy. Leaves (and fruit husks) typically exude a citrusy, pungent scent.

Leaf and ripened fruit

Flowers. In late spring, flowering begins just as the foliage is beginning to emerge. Flowers are unisexual on the same branch of this mostly monoecious species. Male flowers are borne in clusters along 2” to 4” catkins on last year’s branchlets. Female flowers form at the tip of new branchlets on short spikes, consisting of a green ovary covered in sticky hairs and 2 reddish stigma on top. Once fertilized, the fruit grows into a roundish shape. Butternut (Juglans cinerea) is a close cousin and look-alike to black walnut, and has a sticky, football-shaped fruit in contrast. Butternut also has a regular size terminal leaflet and un-notched leaf scars ridged with whiteish, furry hairs. Black walnut leaf scars, in contrast, have no fuzzy unibrow.

Medicinal herbal healing among Native Americans and traditional herbalists find black walnut tree parts to be useful in treating a host of conditions including ringworm, athlete’s foot, hemorrhoids, and also as use as an insecticide. In modern pharmacology, extracts from various tree parts have isolated multiple bioactive compounds containing antibacterial, anti-inflammatory and antioxidant properties. Studies have shown that eating English walnuts promotes therapeutic effects on many human health conditions including diabetes, decreasing LDL cholesterol, and lowering blood pressure. Helpful compounds like these are the phytosterols, found in high amounts in walnuts. In 2018, a study at the University of Missouri found two varieties of black walnut to contain even higher amounts of phytosterols even than English walnuts.

Fruit Classification aka Botany Fun! Nut or drupe? Walnuts are often referred to as drupes, or drupe-like nuts. Which is it, nut or drupe? What constitutes a drupe, anyway? We’ll be meeting many trees with drupes on our tree trek (i.e. hackberry), so for those interested in botany, let’s take a closer look.

‘Nut’ or ‘drupe’ as describing the fruit of a black walnut all depends on how you define the layers of its pericarp. The pericarp is the protective coating over the seed (ripening ovary) keeping it safe and cozy during development. It usually consists of three layers: the inner layer (endocarp), the middle layer (mesocarp), and the outer layer (exocarp, sometimes called the epicarp). A drupe’s defining characteristic is that its ovary is single seeded and surrounded by a very hard endocarp layer (what we would call the “stone” inside) presenting a soft, fleshy mesocarp layer surrounding it. The exocarp is basically an outer skin layer (the part we can see). The ovary of a true nut, on the other hand, has a pericarp that hardens and becomes tough, like the shell of an acorn, chestnut and hazelnut.

Some botanists have defined black walnut’s soft, fleshy outer husk as part of the pericarp – a crucial distinction. My dad’s 1951 4th Edition, UC Berkeley botany book by Dr. Richard Holman describes the husk as containing the outermost pericarp layer, thus making a walnut, to quote the author, “strictly speaking as part of a drupe”. To me, that bit of clarification suggests why you may come across the walnut described as a ‘drupe-like nut’ or a ‘drupaceous nut’. Currently, the botany department at UW Madison states that the walnut is best referred to as a nut because the “husk” is completely separate from the pericarp and formed instead from the extrafloral bracts, meaning the outer parts of the walnut’s flowers. These bracts form as an accessory around the pericarp. I’m confident that if my dad were to step into any grad school botany class today, his professor would most likely say that it’s best to refer to the walnut as a true nut.

FUN FACT: The winter buds along the twigs of black walnut are naked, interesting because usually the buds of tree species that grow in cold, winter climates have scales to protect them. Black walnut buds are basically the exposed leaves waiting to unfold, protected only by their fuzzy hair covering – their winter coat, so to speak!

Winter Identification

  • Twigs are stout with a light brown, chambered pith.
  • Twigs are light brown.
  • Buds are naked (no scales) large, grayish and fuzzy.
  • Buds are alternate, often superimposed 1 above the other.
  • Leaf scar is notched, resembling a heart-shaped smiley face.
  • Leaf scar has no furry fringed ridge above it.
  • Bark is diamond patterned with thick furrows and ridges.
  • Trunks can grow to 3 feet in diameter.

Black Willow

Also known as: swamp willow
Shape: crown open to spreading; trunk often twisted or leaning
Leaves: alternate, lance-like, finely serrated, up to 4¾” long, similar green on both sides
Flowers: male and female catkins on separate trees; dioecious
Fruit: capsules containing seeds, wind-dispersed in summer on cottony hairs
Fall leaf color: yellow to greenish yellow
Height: 30’ to 60’

Budburst in April

The first and easiest fact that comes to mind about black willow is that it is classified into the Willow family. Thank you! Also classified into the Willow family are the aspens; they’re just in a different genus, Populus. Willows make up the very large Salix genus of the Willow family comprising over 400 species of trees and shrubs worldwide, with no less than 100 species in North America. Whew! This is in comparison to the mere 40 comprising the Populus genus worldwide, with only 8 of those species native to North America. With willows, things can get a bit complicated. It’s just the way they are. For, some willow species can easily hybridize with each other and then naturalize into the landscape. Nonnative willows were introduced from Europe in the early days of colonization, and at least three of these nonnatives are now naturalized in Minnesota. One European variety brought by homesteaders moving west, the whitecrack willow, was already hybridized in Europe before arriving here where it tends to crowd out native species. Despite (or perhaps because of) all this, willows in general seem very well adapted. Their natural variability is their strategy to adapt and survive to their current place in willow evolution. Their story of who they are.

Female flowers accepting pollen in May

Leaves. Both the top and bottom sides of black willow leaves are approximately the same green tone, not lighter on the bottom and darker on top like many other willow species. This is a good clue for identification. Leaves are very finely toothed, long, and narrow, tapering to a pointed tip with sometimes a little extra, tail-like extension extending a bit further. A pair of leaf-like appendages (stipules) often appear at the base of the leaf stalk, though this can show later on in the season. Newly emerging leaves are covered in crinkly hairs that typically do not persist. Mature leaves are shiny and smooth. Leaves emerge at the same time as the catkins.

Life and Habitat. Black willow is a moisture loving tree, growing along lakes, rivers and streams and alongside other moisture loving trees in forested floodplains such as cottonwood, silver maple, green ash, box elder, and river birch. Black willow has a short life expectancy averaging about 65 years, but it can live to 100 or so. It can attain a large trunk diameter of about 30” and can also have multiple trunks from the same root. Highly susceptible to fire, black willow will not usually survive, and the few that do will most likely be immune system compromised. After fire, sprouts will form at the base of stumps and begin new trees. Seeds can also sprout into new trees. In addition, black willow twigs, while flexible, can easily detach from their branch, often falling into the nearby water source this species prefers to grow near. The twigs then float downstream to be caught and easily form roots in some new spot of moist soil to begin anew. Black willow has an extensive system of shallow, interlacing roots that are dense and fibrous. This makes them valuable for erosion control along streambeds, waterways, and other soil stabilization projects.

Female catkin ripening

Flowers. At about 10 years old, black willow starts flowering and producing seed. As a dioecious species, trees are either male or female. The tagged tree in the park is female, opening fuzzy greenish white stamens out of her petalless flowers to collect pollen. If this were a male tree, the catkins would be brightly attractive in a showy yellow enticing pollinators to the nectar and pollen before moving on to the female flowers for further nectar replenishment and dropping off pollen at the same time. Look for leaves to emerge at the same time as the catkins.

Fruit. Each female catkin produces many fruits in the form of capsules, yellowish when mature, inflated sort of in a pear or bottle shape with a long beak. At maturity, the capsules split open to release the large quantity of seeds inside, each attached to a fluffy, cottony filament.

Wildlife. Willow seeds, buds and twigs are hugely important to a variety of mammals. Grouse rely on willow buds in spring. Rodents often chew on the bark. Beaver along with deer and moose browse on the leaves in summer and the twigs in winter. Willow trees open their flowers in early spring in the form of catkins. These are replete with nectar and (in males) pollen to attract small insects, which in turn feed hungry bird migrants newly arrived to their nesting areas during that time of year. Birds enjoy eating the catkins and buds as well, and the fluffy stuff from the catkins makes soft, cozy linings for their nests. The tiny, abundant seeds that ripen and scatter into the forest duff below add to the rich leaf litter that sustains insects and again provides forage for other wildlife into the winter.

Seeds dispersed in June

Willows in general are 2nd only to the oaks in the number of caterpillars for which their leaves serve as host. In Minnesota, according to Dr. Doug Tallamy, author and Professor of Entomology, the story is a bit different. Here, willows are even more important than oaks, supporting no less than 359 species of caterpillars on their way to becoming moths and butterflies compared to oak’s 317. Looking beyond the numbers, what’s going on with oaks and willows that make them so important to wildlife? Leaves of certain trees (depending on species) provide food for caterpillars during this very important part of their life cycle. As their bodies turn plant energy into proteins, caterpillars attract wildlife into the trees or in the leaf litter below to feed on them. These include songbirds, turtles, foxes, voles, mice, and black bears, as researched by Dr. Tallamy.

One of my favorite butterflies is the mourning cloak, one of the first butterflies you will see in early spring. After hibernating in the deep, furrowed folds of mature tree bark such as on hackberries and elm, adults emerge very early on some warm, late winter day. The adult females then lay their eggs, typically around the twigs of one of their preferred species — black willow being one of them– before replenishing, perhaps on a drip of sugary sap from a nearby tree.

Medicine. The bark of black willow (and many other willow species) contains salicin, first isolated from the Salix genus in the early 1800s, and thus from which the name ‘salicin’ derives. Salicin means ‘willow’ in Latin. The bark, when chewed, tastes bitter. When salicin is metabolized in the body it converts to salicylic acid, a similar compound found in aspirin. Nature provides much more complexity than isolated extractions, however, offering a conglomerate of antioxidants and anti-inflammatory properties that need to be understood as a whole. As such, herbal healers including Native Americans highly experienced in this type of healing, traditionally use black willow for treating a wide range of medical conditions beyond pain relief.

Uses. The wood is light, straight grained, shock resistant, and does not splinter easily. Pounding in nails will not split willow wood, but it is also relatively weak. As such, it is valuable for cabinets, paneling, tabletops, boxes, crates and light load pallets. Black willow wood takes stain well and can be turned for decorative pieces, toys and the like. Because the wood will not split when nailed and also because of the flexibility of the twigs and branches, they are often used to make rustic bent furniture and baskets. Historically, settlers used black willow as one of the preferred species for converting into charcoal in the making of gunpowder.

Winter Identification

  • Terminal bud is absent.
  • Lateral buds are small with only a single scale.
  • Buds are sharply pointed, reddish brown, pressed closely to twig.
  • Twigs are reddish brown.
  • Bark is thick and fibrous with wide ridges covered by shaggy scales.
  • Bark varies from light to dark grayish brown.
  • Trunks can be large, growing to about 30” in diameter.
  • Often has multiple trunks from the same root.

Blue Beech

Also known as: musclewood, American hornbeam, water beech
Shape: round and full; can have single or multiple trunks
Leaves: simple, narrowly ovate, finely doubly toothed, alternate
Flowers: catkins, male and female separate on same branch; monoecious
Fruit: small, greenish, hairy nutlet attached to a 3-lobed, leaf-like bract
Fall leaf color: brilliant orange, golden yellow to amber, reddish or purplish hues
Height: 20’ to 35’

Pollen catkins forming in spring
Female flower in spring

This slow growing, shade loving understory tree has very dense wood, just behind the hardness rating for Minnesota’s other native understory tree, ironwood (Ostrya virginiana). Blue beech prefers moist soils in a variety of forested sites, especially along streams and forested floodplains but can grow in drier soils as well.

Both blue beech and ironwood are in the Birch family, though they each belong to an entirely different genus. Like other Birch family members, blue beech produces dangling clusters of flowers called catkins, has double serrate leaves, and is monoecious, meaning both male and female flowers are located on the same tree. Due to the very dense, hard wood that both blue beech and ironwood possess, they share a similar common name with ‘hornbeam’ in it. This can be confusing. Blue beech is known as American hornbeam due to the extreme hardness of its wood and a fine grain that polishes up to resemble horn. (‘Beam’ means ‘tree’ in Old English.) Here’s where things can get tangled. Ironwood is also a very hard wood, harder in fact that blue beech, and is known as American hophornbeam. The addition of ‘hop’ is due to the fact that ironwood nutlets are embraced in leaf-like bracts resembling the leafy, bracted fruit of common hops. Blue beech also has bracts holding its seeds, but they are shaped a bit differently in 3-lobed bracts – actually quite lovely!

Closeup of female flower

Blue beech is not in the Beech (Fagaceae) family. Because the leaves and bark at first glance can resemble that of a true beech, such as American beech (Fagus grandifolia), some confusion can arise here as well. Fortunately, blue beech can be distinguished from American beech in a few ways, notably by comparing their different leaf margins, bud shape and fruit. At this point, it may come as a relief to know that both blue beech and ironwood have at least one very distinct difference by which you can tell them apart. The bark on their trunks are vastly different. Blue beech is a very touchable tree with thin, gray bark over wood that has flares rippling like sinew along its length, seeming to invite hands to run along its smooth surface. For this reason, it is also called ‘musclewood’. Simply observe the smooth, sensual bark of the blue beech as opposed to the shreddy textured, vertically rectangular plates of ironwood and you will be well on the way to a deeper understanding of these two species of a different genus that belong to the same family.

Nutlets forming early summer

Leaves are oblong and doubly serrated, 2” to 4” long with prominent veins. Look for the underside of the leaf to be dotted with tiny, dark brown glands. The leaves on a blue beech tree can sometimes be deciduous, but typically the leaves are marcescent, clinging to the branches through much of the winter depending on the individual tree’s local conditions. The winter leaves turn a beautiful shade of amber brown to reddish russet brown, adding spots of color to the understory of the forest against the whiteness of the snow. Equally decorative are the very slender twigs – so lacelike and delicate!

Flowers. Most members of the Birch family produce their male pollen catkins in an immature form in the fall to remain dormant on the twigs through winter. You will not, however, see male catkins on a blue beech in winter. Fun Fact: blue beech male catkins emerge and develop along with the female catkins in the spring.

Blue beech flowers are unisexual, meaning the male flowers are separate from the female flowers. None of the flowers have petals, and the flowers are wind pollinated. In the spring, male flowers form catkins 1¼” to 1½” long, drooping in slender cylinders of yellow green flowers on side branches. Female flowers spiral down in a drooping catkin at the tips of terminal branchlets, at first ½” to 1” long, then maturing to 1¾” long in fruit. Each receptive flower has a hairy, leaf-like bract (that later grows into a 3-lobed bract) with two red styles waiting to catch pollen.

Fruit beginning to mature

Fruit of the blue beech hangs in clusters consisting of leaflike bracts, each with a nutlet about ⅓” long attached to the outside that turns brown when ripe. The bract may act as wing in aiding seed distribution by wind later when the seed ripens in late summer into autumn. Along with the marcescent leaves, these bracts can persist through winter as well. Look closely at the interesting structure of the nutlets. They are oblong and striped with ribs. The shape of the 3-lobed bract also catches your eye with its long, larger center bract rising above the nutlet like a chair back.

While seedlings do form and germinate from fallen nutlets, many blue beech trees also sprout as root suckers from long horizontal roots just below the surface soil, forming colonies of clones all connected underground.

Wildlife. What forest creatures eat blue beech nutlets? Ruffed grouse, wild turkeys, rabbits and squirrels all enjoy them. Other parts of blue beech offers additional sustenance as well, with twigs and leaves attracting cottontails, beaver and white-tailed deer. Leaf buds are a source relied upon by ruffed grouse.

Uses. Trunks rarely grow wider than about 5“ in diameter (though can grow to 12”), so this is not a tree used for commercial lumber. Its close-grained, heavy, hard and strong wood, however, is highly valuable for smaller items such as tool handles, wooden cogs, mallets, and wedges. Its extreme hardness makes this species of tree an excellent source for slow burning fuel in wood stoves.

Doubly toothed leaves
Doubly toothed leaves
Ripened fruit
Ripened fruit
Bracts persisting in winter
Bracts persisting in winter

Winter Identification

  • Leaves often remain on the tree through winter.
  • Male catkins are absent from twigs during winter.
  • Buds are alternate, zig zag, and are held close to the twig.
  • Buds have multiple scales, and their edges are hairy.
  • Twigs are very slender.
  • Twigs are tan to brown with white lenticels.
  • Bark is thin, light to bluish gray, smooth and tight to the wood.
  • Wood of the trunk underneath bark is rippled, fluted and sinewy.

Bur Oak

Also known as: mossy-overcup oak
Shape: rounded, lower branches often spreading horizontally
Leaves: alternate; 5 to 9 round lobes, narrower at the base with a fan-shaped crown
Flowers: male catkins and female flowers on same tree, petalless; monoecious
Fruit: acorn with a fringed cap that covers half or more of the nut
Fall leaf color: golden to yellow brown
Height: 50’ to 80’, occasionally over 100’

Budburst in April

Bur oak belongs to the white oak group and is the most widespread oak species found in Minnesota. Oak trees in general are divided into two groups, white and red, and are easily distinguished by their leaves. Trees in the white oak group all have leaves with rounded lobes while red oak group leaves have lobes that are pointed. White oak acorns mature in one year, whereas red oak acorns take two. Acorns differ as well, with white oak acorns on average producing less tannins and therefore tasting sweeter than red oak acorns. Red oak acorns are higher in tannin content and therefore taste more bitter. Along with the variation in tannins, it makes sense that the acorns in the two groups vary nutritionally. White oak acorns, for example, have lower fat than red. Whether from red or white oak trees, however, all acorns are full of protein, carbs and fats which supply abundant nutrition to the wildlife depending on them.

Baby leaves early May

Bur oak has a superhero toughness in its ability to withstand cold, drought and temporary flooding as well as challenges that urban conditions present. The bark is quite fire resistant. In addition, bur oak sends down a deep taproot with an extensive root system that makes it shelterbelt worthy, another aspect of its adaptability and hardiness. The northernmost range for bur oak covers lower Canada extending from Saskatchewan to Nova Scotia, into Pennsylvania, east to the Midwest and south to Texas. Like other oaks, bur oak can be quite long lived, often for hundreds of years.

Wildlife. Oak trees are an important component of the forest web of life and support a tremendous variety of wildlife. Dr. Doug Tallamy, author and Professor of Entomology, states that oak trees in general support 534 species of moth and butterfly caterpillars. Squirrels, songbirds, great horned owls and other nesting or visiting creatures fill the branches with life and sound day and night. Strong oak branches provide the sturdy roosting spots wild turkeys need at night for their safety and survival. The scrabbling sounds of tiny claws of small mammals and songbirds add to the commotion. The plethora of acorns in autumn continues the attraction. White-tailed deer can’t stay away from this important fall crop, nor can wild turkeys and black bears. Wild turkeys just swallow the acorns whole. Some creatures, such as blue jays, lack the ability to chomp down whole the comparatively thin-shelled nuts and must crack them open first or carry them away for caching. Caching is a good thing for oaks, for if a blue jay or small mammal forgets where he hid some for winter, come spring a bur oak seedling may just have a new locale in which to germinate.

Male pollen catkins

Leaves. Budburst for bur oak starts in late April into May. A typical bur oak leaf has a fan or crown shape at its tip with a very deep sinus lobe cutting in almost to its midrib at the center point of the leaf. Continuing with the superhero analogy, most leaves display a Superman body with a burly chest on top going down to a little waist with slim (albeit lobed) hips below. I’ve also come across some amazingly huge bur oak leaves about 10” long! On average, if you fold a bur oak leaf in half from top to bottom, the deepest sinus will be in the middle. Leaves, however, can show lots of variation. Not all of them present that distinctive crown, and leaves growing in deep shade will often have very shallow lobes similar to the look of a swamp white oak leaf. The underside of the bur oak leaf is densely and uniformly covered with tiny hairs. While all oak trees have the potential to display some degree of marcescence (meaning their leaves dry but remain attached to the twigs in winter) healthy bur oak trees do not do this. In winter, bur oak presents a stark silhouette bare of leaves. Other oak species, especially in the red oak group, keep some or most of their leaves in a decorative display until spring. The dried leaves of bur oak are highly flammable.

Female flowers

Flowers. Flowers form just after the leaves have emerged. The flowers are unisexual, with male and female flowers separately located on the same branch. Female flowers (pistillate) are green tinged with red. Male flowers (staminate) are yellow green on 2 to 4 inch long drooping catkins. The females with their short stalks cluster in small groups in the leaf axils of new growth. Neither sex has petals. Flowers are wind pollinated but need another bur oak to produce seed. Self-fertilization within the same tree is avoided because the flowers of both sexes mature at different times, with male flowers on a given tree pollinating before the tree’s female flowers are ready.

Spent pollen catkins

Fruit. Bur oak begins producing acorns at about 35 years old. Acorn size varies (even within an individual tree), but bur oak is known for producing the largest size acorns of all the native oaks, up to 2” in its southern form. (In the Latinized form of Greek, macro means ‘large’ and carpa, ‘fruit’.) The northern form of bur oak that grows in Minnesota has much smaller sized acorns at ½” to ¾” long. The common name of bur oak pertains to the furry fringe along the cap or cup which slightly resembles the spiny bur found on chestnuts. The coarsely scaled acorn top with its furry fringe covers at least ⅓ of the nut, sometimes all of it. The inside of the cup is typically lined with tiny hairs. Bur oaks have mast years where they produce a huge amount of nuts every 2 to 5 years. Unlike other oaks in the white oak group that germinate right after they fall from the tree (including southern bur oaks), the acorns in our northern form of bur oak germinate in the spring after a period of cold stratification first.

A happy summer leaf

Bark. On young bur oaks, the bark is smooth and stiff, not flaky and peeling like that of swamp white oak. Twigs and young branches of bur oak are covered with corky wings and ridges that are strongly attached. Mature bark is deeply furrowed.

Oak savanna. Bur oak often grows in open areas and loves direct sunlight. The thick, deeply furrowed bark that develops on mature individuals is fire resistant, leaving large loners to stand out here and there after natural wildfires sweep through. The strong roots of this species also allow bur oaks to easily compete with grasses. Up until the time of settlers, wildfires were a natural occurrence that kept these types of areas open and parklike. Fire allowed the regrowth of sun-loving plants such as, for example, our native wild lupine — sole host for the endangered Karner blue butterfly. This habitat, known as oak savanna, was once quite common across southern Minnesota, but with the arrival of settlers imposing fire suppression these areas began to become overgrown with trees and shrubs crowding out sun loving plant species that grow in oak savannas. Red headed woodpeckers are another species frequently found in oak savannas, feeding on acorns and nesting in the cavities that dead oak branches and trunks provide.

Leaf Underside

Uses. Bur oak is a hardwood with qualities similar to white oak, valuable for building construction, cabinetry, barrels, hardwood flooring, furniture and fence posts.

Pests. Like all tree species, oaks have their particular fungal and insect pests, some more pesky than others. In Minnesota, bur oak is typically of the variety Quercus macrocarpa var. oliviformis and is susceptible to bur oak blight caused by a native pathogenic fungus. Bur oak blight is common, and most trees can handle it, but not all; a severely stressed tree can become more vulnerable to other pests and diseases due to a weakened immune system. Another fungus, also native and basically harmless, causes the outer bark to slough off in small areas, leaving smooth, whitish patches showing on the trunk.

Leaf variations

More deadly is a fungus that affects all oaks, including bur oak, causing the fatal tree disease, oak wilt. In the short term, red oak species are more severely affected and die within months after infection. Trees in the white oak group will experience mortality, but it will take longer, sometimes up to 20 years for them to succumb. Bur oaks on average fall in between that range, dying within 1 to 7 years after infection. One way to protect oak trees from oak wilt is to never prune them between April and July, a timeframe during which open wounds make them most vulnerable to infection.

Minnesota bur oaks can be attacked by the two-lined chestnut borer which chews underneath the bark at terminal branches from the tip inwards, killing the tree. This native beetle attacks all oaks, with red oak, again, being the preferred host.

Superman leaf
Superman leaf
Acorns
Acorns
Fruit forming early June
Fruit forming early June
Squirrel at home
Squirrel at home
Acorn in early August
Acorn in early August

Winter Identification

  • Buds are clustered near the terminal end of the twig.
  • Buds are small and rounded with gray fuzz.
  • Twigs are stout, yellow-brown and smooth.
  • Older twigs often are roughened and corky (not peeling).
  • Younger bark is smooth and stiff.
  • Mature bark is gray, thick, and deeply furrowed with coarse, scaly ridges.
  • Bark will often have smooth, whitish patches from a harmless fungus.

Cucumber Magnolia

Also known as: cucumbertree, cucumber tree
Shape: pyramidal to rounded; open crown in maturity
Leaves: simple, alternate, entire, 6” to 10” long tapering to a fine point
Flowers: 2” to 4” wide with greenish white petals, slightly fragrant; monoecious
Fruit: elongated seed pods, red when ripe
Fall leaf color: brownish yellow
Height: 40’ to 80’

Young fruits in early June
Leaf size

The cold hardiest of all the magnolias, cucumber magnolia’s native range extends from mostly mountainous regions of eastern N. America in the Appalachians, west to Louisiana and Missouri to the Ohio and Mississippi River valleys, and as far north as southern Ontario. While not native to Minnesota, the spectacular height of Como Park’s two very mature exemplars shows how well this tree can thrive here, provided they are planted in the cool, moist soil they prefer and with room to spread their roots. Trunks can grow up to 4’ in diameter. The species has very few pest or disease problems.

Seed pod in June

Where does cucumber magnolia get its common name? A quick inspection within the upper branches of these majestic trees will provide the answer. Hiding among the large leaves are an abundance of cute little seed pods resembling cucumber pickles. After flowering is finished in spring, the elongated, cylindrical pods form, green at first, usually somewhat irregular in shape, 1.5” to 3” long, and ripening to a showy red in autumn. When ripe, the pods split open on one side to send out bright orange seeds that dangle from thread-like filaments. The outer seed coat of these attractive seeds is fleshy, oily and soft. Songbirds such as grackles and blackbirds enjoy the young fruits as well as the ripened seeds, as do squirrels and other rodents. The ripened seed pods also sometimes fall to the ground with their seeds still intact, providing welcome forage for ground-feeding birds such as towhees, ruffed grouse and wild turkeys as well as small mammals. Seed dispersal is accomplished by songbirds eating the flesh and then excreting the intact seed. This may also happen with mammals if their teeth don’t damage the seeds, or if some of the seeds pass through uneaten. Water and wind also play their part in dispersing seeds. Lying fallow over the winter, the seeds then cold stratify, making them ready to germinate the next spring.

If you think this unusual floral structure belongs in a movie depicting a prehistoric landscape complete with dinosaurs, then you are right! Many tree species on our planet have indeed been around a very long time. The magnolia is considered to be one of Earth’s first flowering trees dating back about 100 million years; however, these were not the first seed-bearing trees to arrive. The first seed-bearing trees were conifers, ginkgos and cycads — nonflowering species appearing over 300 million years ago. These first trees were so successful at seed production that they developed and thrived over several periods of geologic time; by the Early Cretaceous, conifers and their relations dominated Earth’s landscape alongside the dinosaurs. Subsequent to these nonflowering trees, the first flowering trees (including those in the Magnolia family) appeared in the fossil record dating back to the Cretaceous Period. This distinction of flowering vs. nonflowering is one of the very basic characteristics used in botany for classification. A flowering tree, called an ‘angiosperm’, has an ovule (undeveloped seed) that remains protected inside the ovary of each flower. ‘Angiosperm’ translates as ‘vessel seed’, this as opposed to the ovule hanging open to the air in a cone as with the nonflowering trees, the gymnosperms (translating as ‘naked seed’).

Ripe seed pod

The naked seeds of gymnosperms rely mostly on wind for pollination while the flowers of angiosperms rely on wind, insects or both. Cucumber magnolia steps in here as part of the long line of ancient plants in the Magnolia family relying on beetles for pollination – the insects that were plentiful at the time magnolia was first evolving. Beetles and these first flowers evolved together. Flying insects we’re more likely to think of as pollinators (such as bees, moths and butterflies) were still millions of years away from their own sorts of specialist relationships alongside more complicated flower structures in the making. Since beetles are poor and clumsy fliers and others are actually flightless, magnolia flowers evolved a structural design over time to best attract beetles. As a consequence, magnolia and other ancient lineages (such as water lilies) offer flowers that are wide, light colored, and filled with protein-rich pollen beetles love. The widely spaced, easily accessible petal arrangements of these first flowers remain basically the same as we see them now. Each spring as it has always done through millennia, cucumbertree opens its durable, bowl-shaped flowers wafting out a spicy aroma that beetles can’t resist, advertising that the restaurant is open. Pollen mostly, not nectar, is what these hungry beetles are looking for as they clamber in and out of the many light-green, 3” wide bowls of food on offer, transferring pollen along the way just as they have done across the vast span of time and continue to do so today.

Seed and filament

Leaves. Cucumber magnolia has a pleasing, overall symmetrical shape with beautiful foliage casting dense shade. Leaves are dark green, and 6” to 10” long tapering to a fine point. The edges of the leaves are smooth. They are also undulate, which means they have a natural wave to them which can make them difficult to press. In Latin, acuminata means ‘pointed’.

Cucumber magnolia trees begin to produce seed at about 30 years of age. The flowers are greenish white, in the light color range beetles seem to prefer. Flowers last for 3 to 4 days, opening in the morning and closing at night. Cucumber magnolia is monoecious, meaning both male and female reproductive parts are on the same tree; therefore, all cucumber magnolia trees can produce fruit. The individual flowers, however, are self-incompatible even from their own tree, and need pollen from a nearby tree to produce viable, abundant seed. (Loner trees can produce less viable fruit with other flowers on the same tree if that’s all that’s available.)

Overwintered fallen seed pod

Individual flowers have one or two special strategies to avoid fertilizing themselves. One especially tricky strategy involves the female and male parts ripening at different times within an individual flower. Female parts are only receptive on the first day. Beetles entering a flower that has receptive female stigmas bring in pollen from a previous flower’s anthers that are still messily sticking to their bodies. There may be a few yummy floral parts to gnaw on and some stigma secretions to keep them busy for a while, even overnight and trapped within the closed petals. When the petals open again the next day, the female parts are no longer receptive, and that flower’s anthers are now ripe and producing pollen. The beetle stays to feed on the new pollen, then departs and transports it to the next flower.

Stout twigs silhouette

Medicine. Recent scientific studies using extracts of the inner bark of Magnolia acuminata identified two phenolic acids and three catechins. These types of compounds have strong antioxidant and anticancer properties. Catechins, for example, are the major flavonoids found in green tea. The knowledgeable traditions of Indigenous Peoples reveal great experience with the inner bark of magnolia tree. Healers would scrape it out to employ its healing properties for use in the treatment of several maladies. These include providing pain relief from toothache, muscle aches, pain and fever as well as a treatment for internal parasites.

Winter Identification

  • Buds alternate on stout, reddish brown to gray twigs.
  • Leaf scar is a slender U-shaped curve with 5 to 9 vein scars.
  • Terminal bud has one solitary, hairy bud scale.
  • Twig pith is white.
  • Bark is rough and furrowed with flattened ridges.
  • Trunk diameter can reach 3 to 4 feet.

Eastern Red Cedar

Also known as: red juniper, aromatic cedar
Shape: pyramidal
Leaves: 2 kinds, juvenile and adult
Strobili: females yellowish green; males mustard yellow; dioecious 
Seeds: 1 to 3 inside ¼” wide, dark blue, berrylike cone
Fall leaf color: leaves take on a bronze tint in winter
Height: 10’ to 60’ in Minnesota, typically

Pollen cones mid March

When identifying eastern red cedar (Juniperus virginiana), look for two kinds of leaf growth. Juvenile leaves, called ‘whips’, are fast growing shoots with short, sharply tapering leaves less than ⅜“ long, spreading outward making them feel prickly. Whips most often occur on younger trees, but also appear randomly on trees that are older. Adult leaves are much smoother; their tiny (scant ⅛” long) leaves compactly overlap each other tightly to the twig, making them appear scalelike.

Female conelets early April

Leaf color varies depending on the season. Spring and early summer leaves are green. In winter, the leaves darken to bronzy tints of reddish brown, more easily discernible from a distance. The bark is thin, grayish to reddish brown, and peels off in shreddy, fibrous strips. The bark’s soft nature gives this species little fire resistance. Once ignited, the tree will burn energetically, although if there is little or no vegetation beneath, larger trees may escape complete mortality. Foliage grows densely, providing roosting and nesting cover for birds as well as shelter for mammals in winter.

Female conelets in mid May

Despite its common name, eastern red cedar is a juniper in the Cypress family — not an actual true cedar at all. The aromatic scent emanating from its wood is similar to that of true cedars and so lends itself to the common name. While not very shade tolerant, if given full sun and not much competition with other species, eastern red cedar can grow in many different soil conditions from alkaline to acidic, salty to fertile. In general, it prefers well-drained soil that is not too continuously moist. Eastern red cedar will appear in overgrown pastures and open fields that are not exposed to frequent wildfires, as well as along rocky bluffs, and is often used as a windbreak in shelterbelts. Its native range is roughly the eastern half of N. America, with two recognized varieties in the north and south.

Seed cones developing in early summer

Most evergreen species are monoecious, meaning both female and male flowers are present on the same tree. Some evergreens — eastern red cedar being one of them — share the trait of being dioecious (di, meaning ‘two’) with separate male and female individuals. On first learning this fact I was quite surprised, for prior to that it had never occurred to me that not just animals and birds, but plants also can take separate male and female forms.

Female strobili (seed cones) first form as little more than scale-like swellings on branch tips the previous fall, inconspicuously small and tinted light yellowish green to blue green. In early spring of the next year, these conelets start to develop and enlarge to about 1/16” or so as the many ovules prepare to receive pollen. Like many gymnosperms (plants that are nonflowering), the female cone produces a sap droplet that pulls in the correct species of pollen grain needed for fertilization. Once they are pollinated, the female cones close and begin to develop over the summer slowly maturing from greenish white until ripening deep blue with a whitish, waxy coating. The cones are roundish and fleshy, like berries, but they are not berries. These are the seed cones. At maturity, they are about ¼” in size. Seed cones mature in the same year they are pollinated.

Seed cones in autumn

Male strobili (pollen cones) also begin as undeveloped conelets in the previous fall. Male strobili are about ⅛” across and appear in large clusters on the ends of branches. By late winter, the scales of the pollen cones turn bright yellowish brown as they approach their fully ripened stage, making male trees at this time of year quite conspicuous and identifiable. Then, in May, the pollen cones open to release copious amounts, mist-like and smoky, into the warm springtime wind to disperse over everything including receptive females. When the pollen cones are spent, they turn brown and eventually disintegrate.

Seed cones. A few wingless seeds are inside each cone. When a cone easily separates from the twig, it is ripe (usually autumn through winter in Minnesota) and ready to harvest. Eastern red cedar “berries” are highly valued as flavoring used in small quantities such as in the making of gin, and traditionally added during the cooking of venison and in stews. They are also used to brew medicinal tea. The aromatic oils of both the fruits and leaves are extracted for making medicines and perfumes.

Cedar-apple rust gall winter dormant

Wildlife. Cedar waxwings are named for this tree because the seed cones are one of their favorite foods. These are an important winter staple for them (and for many birds), and this reliance goes both ways. One scientific study shows that the seeds a cedar waxwing excretes tend not only to be better dispersed but also have a higher rate of germination. This dispersion process is also important given the nature of the closed cones and wingless seeds. Bluebirds, warblers, wild turkeys, ruffed grouse, goldfinches, flickers, grosbeaks, robins and other songbirds all join in the feast to gobble up the nutritious cones during autumn into winter. Mammals also relying on these comprise a long list of their own, including bears, rabbits, foxes, raccoons, skunks, possums, coyotes and deer. High in crude fat and fiber, the fleshy cones also contain moderate amounts of calcium.

Cedar-apple rust telial horns mid May

The aromatic wood of eastern red cedar lends itself to the construction of cedar chests (‘hope’ chests), decorative boxes, cabinetry, and the wooden lining for closets. Although a thing of long ago, for many decades before the supply of this sought-after wood became diminished, eastern red cedar was the preferred wood for the manufacture of pencils due to its uniform, fine grained heartwood and pleasant scent. The ability of the wood to withstand rotting makes it valuable for outdoor uses such as fence posts and furniture. Anishinaabe artisans peel strips of eastern red cedar bark, then boil some of them in a dye formula resulting in decorative strips in a mahogany color. Working with these variously colored strips for patterning, they create beautiful anaakan, traditional woven cedar mats.

Gall fully ripened

On a wet, springtime hike, you may come across a cedar-apple rust gall growing on an eastern red cedar branch. This can be rather surprising! Bright orange tube projections, called ‘telial horns’, emerge from the gall in spring and can appear almost otherworldly. In time, their spores will release to travel upwards of two miles. The complicated cycle of this fungus involves stages taking place on both apple and eastern red cedar trees. The fungus lives on an apple leaf for a few months and then is wind borne to an eastern red cedar in late summer where it forms the brown gall that overwinters many months on the branch until it blooms again the following spring, thus carrying on the cycle. Because of this disease, it may be a good idea not to locate an eastern red cedar tree very near an apple tree, if you can help it.

Two kinds of leaves
Two kinds of leaves

Winter Identification

  • Bark is gray to reddish brown, peels in fibrous strips.
  • Mature leaves are green to blue-green, stiff, overlapping, scalelike.
  • In winter, leaves may show bronzy, reddish-brown tints.
  • Newer leaves consist of prickly whip shoots.
  • Berrylike cones often remain on tree through winter.
  • Twigs are reddish or grayish brown.
  • In late winter, male pollen cones brighten to yellow brown on twig ends.

American Basswood (Tilia americana)
American Linden
44°58’53.6″N 93°08’44.5″W

American Beech (Fagus grandifolia)

44°58’40.2″N 93°08’43.8″W

American Elm (Ulmus americana)

44°58’51.4″N 93°08’53.0″W

Amur Maple (Acer ginnala)

44°58’47.5″N 93°08’42.9″W

Austrian Pine (Pinus nigra)
European Black Pine
Near Scots Pine

44°58’46.5″N 93°08’54.0″W

Balsam Fir (Abies balsamea)
largest one in grove

44°58’46.4″N 93°08’43.7″W

Bigtooth Aspen (Populus grandidentata)
Largetooth Aspen

44.9814699, -93.1492161

Black Locust (Robinia pseudoacacia)

44°58’53.6″N 93°08’42.2″W

Black Walnut (Juglans nigra)

44°58’53.0″N 93°08’43.8″W

Black Willow (Salix nigra)

44°58’47.7″N 93°08’36.8″W

Blue Beech (Carpinus caroliniana)
American Hornbeam
Musclewood

44.981058, -93.1473767

Bur Oak (Quercus macrocarpa)

44°58’54.1″N 93°08’43.0″W

Colorado Blue Spruce (Picea pungens)
Blue Spruce
Colorado Spruce

44°58’49.1″N 93°08’48.5″W

Cucumber Magnolia (Magnolia acuminata)
Cucumbertree

44°58’53.9″N 93°08’44.3″W

Douglas-fir (Pseudotsuga menziesii)

44°58’48.3″N 93°08’47.3″W

Eastern Red Cedar (Juniperus virginiana)
by streetcar station path, near Lexington

44°58’40.8″N 93°08’47.2″W

Eastern White Pine (Pinus strobus)
White Pine

44°58’49.2″N 93°08’57.5″W

Ginkgo (Ginkgo biloba)
Maidenhair

44°58’48.3″N 93°08’53.9″W

Common Hackberry (Celtis occidentalis)

44°58’49.3″N 93°08’39.0″W

Honey Locust (Gleditsia triacanthos)

44°58’49.3″N 93°08’53.6″W

Ironwood (Ostrya virginiana)
American Hop-hornbeam

44°58’50.9″N 93°08’43.8″W

Kentucky Coffeetree (Gymnocladus dioicus)
Female tree on hill behind catalpa

44°58’57.1″N 93°08’43.7″W

Kentucky Coffeetree (Gymnocladus dioicus)
Male tree by pedestrian bridge

44°58’52.6″N 93°08’42.7″W

Northern Catalpa (Catalpa speciosa)
Cigar Tree
1 of 2

44.98207, -93.14558

Northern Catalpa (Catalpa speciosa)
Cigar Tree
2 of 2 (by Ironwood tree)

44°58’50.7″N 93°08’43.8″W

Northern Red Oak (Quercus rubra)
Red Oak

44°58’52.5″N 93°08’44.6″W

Northern White Cedar (Thuja occidentalis)
Arborvitae
by lily pond

44°58’50.7″N 93°08’47.2″W

Norway Spruce (Picea abies)

44°58’49.2″N 93°08’48.6″W

Ohio Buckeye (Aesculus glabra)

44°58’51.5″N 93°08’45.6″W

Paper Birch (Betula papyrifera
White Birch

44.9780151, -93.1475098

Ponderosa Pine (Pinus ponderosa)

44°58’48.6″N 93°08’44.9″W

Red Pine (Pinus resinosa)
Norway Pine

44°58’47.7″N 93°08’51.9″W

Red Maple (Acer rubrum)

44.9793755,-93.1450108

River Birch (Betula nigra)

44°58’47.0″N 93°08’39.8″W

Rock Elm (Ulmus thomasii)

44°58’42.1″N 93°08’47.3″W

Scots Pine (Pinus sylvestris)
Scotch Pine
top of hill, head of grove

44°58’45.6″N 93°08’52.6″W

Silver Maple (Acer saccharinum)

44°58’50.3″N 93°08’53.2″W

Sugar Maple (Acer saccharum)
Rock Maple
2nd one in grove

44°58’47.7″N 93°08’39.8″W

Swamp White Oak (Quercus bicolor)

44°58’40.2″N 93°08’43.6″W

Tamarack (Larix laricina)
Too small to tag; just for map

44°58’53.6″N 93°08’45.0″W

White Fir (Abies concolor)

44°58’48.2″N 93°08’46.5″W

White Mulberry (Morus alba)

Not tagged, near tagged White Pine
44.980666, -93.149716

White Poplar (Populus alba)

44°58’50.2″N 93°08’38.3″W

White Spruce (Picea glauca)

44°58’49.2″N 93°08’48.7″W

Pre-2021 tree list

  • Austrian Pine
  • Black Locust
  • Black Walnut
  • Bur Oak
  • Catalpa
  • Douglas Fir
  • Green Ash
  • Hackberry
  • Honey Locust
  • Kentucky Coffee
  • Magnolia
  • Mulberry
  • Ohio Buckeye
  • Ponderosa Pine
  • Red Oak
  • Scotch Pine
  • White Fir
  • White Pine