winter twigs

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Winter Trees and Shrubs: Box Elder

Box elder is a maple that doesn’t often get credit for being a maple. Moreso, it is a tree that is not thought highly of, and it may not even be welcome in certain discussions around maples. You could even say that box elder is a “rogue maple,” as Arthur Plotnick deems it in The Urban Tree Book. It should come as no surprise, but if people are going to talk about a plant this way, it’s only going to make me like it more.

First off, the leaves of Acer negundo are palmately compound, compared to the simple, palmately lobed leaves of other maples. A box elder leaf is generally composed of three leaflets, sometimes five or seven. The center leaflet is on a longer stalk than the side leaflets, which are oppositely arranged. Sometimes the leaves are confused with ash tree leaves (Fraxinus spp.), which is the reason for another common name, ash-leaved maple. It’s also not uncommon for box elder leaves to be mistaken for poison ivy, which is maybe not a plant you’d want to be confused with. In the fall, unlike the beautiful reds, oranges, purples, and yellows of so many other maples, the leaves of box elder turn a drab yellow before dropping, a trait that Plotnick calls “an embarrassment.”

leaf of box elder (Acer negundo)

It’s not really its leaf, however, that bothers people. Box elder is a fast-growing and prolific tree. Basically, it’s weedy, and because it grows so quickly, its wood is generally weak and its structure unpredictable. It falls apart easily, and it doesn’t always grow in typical tree fashion. Sometimes its more of a shrub, and sometimes it leans so far over that it practically lies on the ground. It sprouts and suckers in abundance, and as John Eastman puts it in The Book of Forest and Thicket, it “generally ignore(s) human standards for an attractive tree.”

Maybe before people knew better, or during a time when people just needed a fast growing tree to plant in their developing cities, box elders were widely planted across North America and beyond. That and their ability to spread readily helps to obscure their native distribution. Box elder is naturalized across North America, but its original distribution (whatever that means) appears to be more midwestern and eastern. Box elder grows in a variety of conditions, and is actually quite drought tolerant, which has allowed it to feel right at home in the American west, whether it is truly native here or not.

Identifying box elder in the winter can be pretty easy, especially if you come across a seed-bearing individual. Box elders are dioecious, meaning male and female flowers occur on separate individuals (another thing that sets them apart from other maples). A samara-bearing tree is a female tree, and the samaras often hang from the branches in great numbers. Like other maples, the fruits are paired together, each seed with a prominent wing. The samaras of boxelder point downward and hang from long stalks, persisting on the tree throughout the winter.

persistent samaras of box elder

The twigs of box elder are glaucous (covered with a thin, powdery bloom) and can be either green, bluish-white, or reddish-purple. They have tiny, white lenticles, and their buds are oppositely arranged. Leaf scars are a broad U-shape, and scars opposite of each other meet at the tops of the U’s, coming to a raised point. At least three bundle traces (sometimes more) are visible in the scar. Leaf buds are protected by two scales that are covered in dense, white hairs. The scales are similar in color to the twigs, but appear more white due to the fuzz. Lateral buds are 1/8 inch long or longer. Slicing open the twigs lengthwise reveals solid, white pith in the center that blends in easily with the wood.

winter twigs of box elder
winter twigs of box elder, pith exposed

The bark of young box elders has slight vertical ridges and is light brown or grey-brown, with dull orange, raised, wart-like lenticels. It is finely scaly. The scales and ridges become more rough and blocky as the tree ages. Mature bark is light brown to grey and heavily furrowed, with blocky segments breaking apart horizontally.

maturing bark of box elder

A few years ago I was introduced to a massive box elder in Boise, Idaho. It quickly became my favorite tree in the area, and I visit it frequently. For all the hate that box elder can receive, seeing its potential to create an experience that few other trees in the area offer can send all of that negative talk out the window. Visit something like it yourself sometime, and see what it can do for you.

massive box elder

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Winter Trees and Shrubs: Sweetgum

Sweetgum is a distinctive tree at any time of year. It stands out among most other deciduous trees with its excurrent growth habit, which gives it a narrowly conical or pyramidal shape. Only in its advanced age does it begin to develop a more rounded and irregular form. Its leaves are star-shaped with either five or seven lobes and span between four and seven inches. Their glossy green color gives way to a wide range of colors in the fall, including yellow, orange, red, and maroon, remaining on the tree for several weeks depending on weather conditions. The fruits are particularly distinct, especially in the winter after the leaves have dropped. Woody balls made up of a series of capsules with pointed beaks hang from long stalks throughout the winter, windborne seeds having been released from small openings in the fall. Without even bothering to look at the twigs, seeing these durable, spiky balls hanging from branches (or feeling them under your feet) is a quick indication that you are looking at a sweetgum.

one of many fall colors found on sweetgum (Liquidambar styraciflua)

Liquidamabar styraciflua (one of the funnest botanical names to say) was previously placed in the family Hamamelidaceae but is now one of the few members of Altingiaceae. Its natural distribution is broad, covering a large portion of the eastern United States and west into Missouri then down into Texas, Mexico, and much of Central America. Outside of its natural range it has been widely planted as an ornamental, and there are several popular sweetgum cultivars currently in cultivation. Both the common and botanical names for this tree refer to the resin found in its bark, which historically has had many uses.

The winter twigs of sweetgum are stout, round, smooth, and yellow-brown to green or olive-green to brown-purple in color. They can also be glossy and feature a few scattered lenticels. Older twigs (or branchlets) are brown at first and then light grey with dark grey lenticels. They are occasionally adorned with corky wings similar to those of bur oak. Because the wings aren’t always present, it can be a fun thing to encounter when you are out looking at twigs.

corky wings on the branchlets of sweetgum

The winter buds of sweetgum twigs are egg-shaped and made up of bud scales with acute tips and ciliate margins. They are green to orange-brown or reddish in color and occasionally sticky. Lateral buds are alternately arranged, are much smaller than terminal buds, and are stalkless and flattened against the twig. They sit above a slightly raised leaf scar that is half-elliptical to triangular in shape and has three distinct vascular bundle traces. The pith of sweetgum twigs is solid, continuous, brownish, and irregularly shaped.

winter twig of sweetgum tree

Sweetgum bark is light to dark grey and is made up of a series of rough, vertically arranged, scaly ridges that become deeply furrowed with age. The mace-like fruits of sweetgum are about one inch wide and, at a glance, are similar in appearance to the seed balls of sycamore trees; however, sycamore seed balls easily break apart when compressed, while the pointed, woody capsules that make up a sweetgum ball are held firmly together and can hold their shape for long periods of time. When these “gumballs” collect on the ground below, they can become a hazard, especially where there is lots of foot traffic. Speaking from experience, they are also obnoxious when operating a mower. This polarizing feature has resulted in bad opinions of the sweetgum tree. Luckily, some people are out there defending it.

sweetgum bark
the persistent fruits of sweetgum

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Winter Trees and Shrubs: Kentucky Coffeetree

A few years ago, I was on the hunt for a Kentucky coffeetree. I was aware that a few could be found in some of the parks around Boise, but not being familiar with them, I wasn’t sure where exactly to find one or what I was even looking for. One winter while riding my bike to work, I noticed a tree at the edge of a golf course. No doubt I had passed this tree hundreds (if not thousands) of times. What caught my eye were thick, bean-like pods hanging from the ends of branches. They were unlike any other tree fruits I was familiar with. I stopped and, with a little effort, knocked one of the pods free from the tree. When I split it open, I found three or four large, smooth, black seeds inside. Later, I confirmed that the tree was indeed Kentucky coffeetree. Passing by it during any other time of year, it may have never caught my eye – just another deciduous tree with green leaves that, from a distance at least, looks like so many other deciduous trees. But in winter, with several chunky pods hanging from the tips of its stout branches, it really stood out. This is the joy of looking at trees and shrubs in the winter, where features that may otherwise be obscured, become glaringly obvious against the plainness of a winter backdrop.

fruits of Kentucky coffeetree (Gymnocladus dioicus)

Kentucky coffeetree (Gymnocladus dioicus) is in the bean family (Fabaceae). It occurs in forests across the eastern and central United States and north into southern Ontario, Canada. It is also planted in urban areas both within and outside of its native range. It is a medium to large tree, averaging 60-70 feet (18-21 meters) high and 40-50 feet (12-15 meters) wide. It generally branches out at around 10-15 feet high and forms a narrow, rounded to pyramidal crown. It is a fairly sparsely branched tree compared to other trees its size, which is much easier to observe in the winter after all of its leaves have dropped.

winter twigs of Kentucky coffeetree

The winter twigs of Kentucky coffeetree are thick and stubby with few hairs and can be greenish, orange, brown, or deep wine-red in color. They have small, scattered lenticels that are either white, orange, or orange-brown. Their leaf scars are alternately arranged and are heart- or sheild-shaped and very large with 3 to 5 distinct bundle traces. It’s pretty obvious from the leaf scars that Kentucky coffeetree bears a sizeable leaf. These massive, bipinnately compound leaves are demonstrated in this Plant Sleuth YouTube video. Leaf buds are tiny and found directly above the leaf scar. There are usually two of them, one of which is sterile and can be difficult to see. They are round, hairy, olive-colored, and sunken like fuzzy, little craters, although you’ll need a hand lens to really see the hairs (which I highly recommend). The twigs lack a terminal leaf bud. Their pith is rounded, thick, and either orange, brown, or salmon colored. The young bark of Kentucky coffeetree is pale gray and fairly smooth. As the tree ages, it breaks into shallow ridges that run the length of the tree. At maturity, the bark is shades of grey and scaly with long, defined, narrow ridges.

pith of Kentucky coffeetree twigs

Kentucky coffeetree is dioecious, meaning that there are “male” trees and “female” trees. The tree that I found on the golf course was a “female” tree because it was bearing fruit, which the “males” and certain cultivars won’t have. If there are no seed pods present, you will have to rely on other features to identify the tree; however, when the pods are present, the tree is unmistakable. Its fruits are thick-walled, flat, oval-shaped, smooth, leathery, and orange-brown to black in color. They measure around 5 to 10 inches long and up to 4 inches wide. They are indehiscent and can persist on the tree for more than a year, and even those that fall to the ground can take months or years to break down enough to release the seeds, which have a hard, dark seed coat. Inside the pod, the seeds are embedded in a thick, gooey, yellow-green pulp, which some descriptions call sweet. However, it doesn’t look appetizing enough to try, and considering that the seeds are toxic, I’d be hesitant to consume any part of the fruit without first verifying its safety with a reputable source. That being said, the seeds can be roasted and used to make a coffee substitute and, as long as it’s done correctly, is safe to drink.

mature bark of Kentucky coffeetree

Kentucky coffeetree is one of the last trees to leaf out in the spring and one of the first to drop its leaves in the fall. Flowers appear in mid to late spring. The leaves have a pink to bronze color as they first emerge, and in the fall they turn bright yellow before they drop.

fall foliage of Kentucky coffeetree

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Winter Trees and Shrubs: Tulip Tree

At first glance, a tulip and a tulip tree couldn’t be more different. One is a bulb that puts out fleshy, green leaves in the spring, topped with colorful, cup-shaped flowers, barely reaching a foot or so tall. The other is a massive, deciduous tree with a broad, straight trunk that can grow to nearly 200 feet tall. But if you can get a look at the flowers, seed heads, and even the leaves of this enormous tree, you might see a resemblance – at least in the shape of these features – to one of our most popular spring flowering geophytes.

Tulip tree (Liriodendron tulipifera) is distributed across the eastern United States and has been planted widely outside of its native range. Also commonly known as tulip poplar, yellow poplar, and whitewood, it is a member of the magnolia family and is one of two species in its genus (the other being Liriodendron chinense – a tree found mainly in China). Many (if not most) deciduous trees of North America have small, inconspicuous flowers, but tulip trees – like its close relatives, the magnolias – have relatively large, showy flowers. The trouble is actually getting to see them since, at least on mature trees, they are borne in a canopy that is considerably taller than the average human.

Tulip tree flowers are cup-shaped, yellow-green and orange, with a series of prominent stamens surrounding the carpels which are attached to a long, slender receptacle giving it a cone-shaped appearance. As the flower matures into fruits, the tulip shape of the inflorescence is maintained as the seeds with their wing-like appendages form a tight, cone-like cluster that opens as the seeds reach maturity. The wings aid in dispersal as the seeds fall from the “cone” throughout the winter.

seed head of tulip tree (Liriodendron tulipifera)

The four-lobed leaves of tulip trees also form a vague tulip shape. They are alternately arranged, bright green, and up to five or six inches long and wide, turning yellow in the fall. Two prominent, oval-shaped stipules surround the stem at the base of the petiole of each leaf. These stipules come into play when identifying the leafless twigs of tulip trees during the winter months.

leaf of tulip tree (Liriodendron tulipifera) in late summer

The winter twigs of tulip trees are easily recognizable thanks to their duck bill shaped buds which are made up of two wine-red, violet, or greenish bud scales. The terminal buds are considerably larger and longer than the lateral buds, some of which are on little stalks. The twigs are smooth, olive-brown or red-brown, with just a few, scattered, white lenticels. Leaf scars are rounded with a dozen or so bundle scars that are either scattered or form an irregular ellipse. Pronounced stipule scars encircle the twig at the location of each leaf scar. Twigs can be cut lengthwise to reveal pale white pith that is separated by a series of diaphragms.

winter twig of tulip tree (Liriodendron tulipifera)
top right: the chambered pith of black walnut (Juglans nigra); bottom left: diaphragmed pith of tulip tree (Liriodendron tulipifera)

The bark of tulip trees can be easily confused with that of ash trees. Young bark is smooth and ash-gray to grayish green with pale, vertical cracks. As the tree matures, the cracks develop into furrows with flat-topped ridges. The ridges grow taller and more peaked, and the furrows grow deeper as the tree reaches maturity. In the book Winter Botany, William Trelease compares the mature bark of tulip trees to a series of parallel mountain ranges with deep gullies on either side.

maturing bark of tulip tree (Liriodendron tulipifera)

Perhaps even as tulips are blooming, the buds of tulip trees break to reveal their tulip-shaped, stipule bearing leaves. This makes for an interesting show. In The Book of Forest and Thicket, John Eastman describes it this way: “from terminal buds shaped like duck bills, successions of bills within bills uncurl and unfold, revealing a marvel of leaf packaging.”

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The photos of tulip tree were taken at Idaho Botanical Garden in Boise, Idaho.

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Winter Trees and Shrubs: Netleaf Hackberry

Boise, Idaho is frequently referred to as the City of Trees despite being located in a semiarid region of the Intermountain West known as the sagebrush steppe where few trees naturally grow. It earns this moniker partly because the name Boise is derived from the river that runs through it (the Boise River), which was named La Rivere Boisse, or The Wooded River, by early French trappers. Although it flows through a largely treeless landscape, The Wooded River was an apt name on account of the wide expanse of cottonwoods and willows that grew along its banks. The fervent efforts of early colonizers to plant trees in large numbers across their new city also helped Boise earn the title, City of Trees. Today, residents continue the legacy of planting trees, ensuring that the city will remain wooded for decades to come.

As is likely the case for most urban areas, the majority of trees being planted in Boise are not native to the region. After all, very few tree species are. However, apart from the trees that flank the Boise River, there is one tree in particular that naturally occurs in the area. Celtis reticulata, commonly known as netleaf hackberry, can be found scattered across the Boise Foothills amongst shrubs, bunchgrasses, and wildflowers, taking advantage of deep pockets of moisture found in rocky outcrops and draws.

The western edge of netleaf hackberry’s range extends to the northwest of Boise into Washington, west into Oregon, and down into California. The majority of its range is found south of Idaho, across the Southwest and into northern Mexico, then east into the prairie regions of Kansas and Oklahoma. Previously placed in the elm family, it is now considered a member of the family Cannabaceae (along with hemp and hops). It’s a relatively small, broad tree (sometimes a shrub) with a semi-rounded crown. It grows slowly, is long-lived, and generally has a gnarled, hardened, twisted look to it. It’s a tough tree that has clearly been through a lot.

The leaves of Celtis reticulata are rough, leathery, and oval to lance shaped with serrate or entire leaf margins. Their undersides have a distinct net-like pattern that gives the tree its common name. A very small insect called a hackberry psyllid lays its eggs inside the leaf buds of netleaf hackberries in the spring. Its larvae develop inside the leaf, feeding on the sugars produced during photosynthesis, and causing nipple galls to form in the leaves. It’s not uncommon to see a netleaf hackberry with warty-looking galls on just about every leaf. Luckily, the tree doesn’t seem to be bothered by this.

fallen leaves of netleaf hackberry (Celtis reticulata) with nipple galls

The fruit of netleaf hackberry is a pea-sized drupe that hangs at the end of a pedicel that is 1/4 to 1/2 inch long. Its skin is red-orange to purple-brown, and its flesh is thin with a large seed in the center. The fruits, along with a few random leaves, persist on the tree throughout the winter and provide food for dozens of species of birds and a variety of mammals.

persistent fruit of netleaf hackberry (Celtis reticulata)

Celtis reticulata is alternately branched. Its twigs are slender, zig-zagging, and often curved back towards the trunk. They are reddish-brown with several pale lenticels and have sparse, fine, short hairs that are hard to see without a hand lens. The leaf scars are small, half-round, and raised up from the twig. They have three bundle scars that form a triangle. The buds are triangle-shaped with fuzzy bud scales that are slightly lighter in color than the twig. The twigs are topped with a subterminal bud, and the pith (the inner portion of the twig) is either chambered or diaphragmed and difficult to see clearly without a hand lens. 

twigs of netleaf hackberry (Celtis reticulata)

The young bark of netleaf hackberry is generally smooth and grey, developing shallow, orange-tinged furrows as it gets older. Mature bark is warty like its cousin, Celtis occidentals, and develops thick, grey, corky ridges. Due to its slow growth, the bark can be retained long enough that it becomes habitat for extensive lichen colonies.

bark of young netleaf hackberry (Celtis reticulata)

bark of mature netleaf hackberry (Celtis reticulata)

Netleaf hackberry is one of the last trees to leaf out in the spring, presumably preserving as much moisture as possible as it prepares to enter another scorching hot, bone-dry summer typical of the western states. Its flowers open around the same time and are miniscule and without petals. Their oversized mustache-shaped, fuzzy, white stigmas provide some entertainment for those of us who take the time to lean in for a closer look.

spring flowers of netleaf hackberry (Celtis reticulata)

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Photos of netleaf hackberry taken at Idaho Botanical Garden in Boise, Idaho.

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Winter Trees and Shrubs: Eastern Redbud

Botanizing doesn’t have to end when the leaves fall off the trees and the ground goes frozen. Plants may stop actively growing during this time, but they are still there. Some die back to the soil level and spend the entire winter underground, leaving behind brown, brittle shells of their former selves. Others, particularly those with woody stems, maintain their form (although many of them leafless) as they bide their time while daylength dips and rises again, bringing with it the promise of warmer weather. Plants that leave us with something to look at during the winter can still be identified. Without foliage or flowers to offer us clues, we rely instead on branches, bark, and buds to identify woody species. In some cases, such features may even be more helpful in determining a certain species than their flowers and foliage ever were. Either way, it’s a fun challenge and one worth accepting if you’re willing to brave the cold, hand lens and field guides in tow.

In this series of posts I’ll be looking closely at woody plants in winter, examining the twigs, buds, bark, and any other features I come across that can help us identify them. Species by species, I will learn the ropes of winter plant identification and then pass my findings along to you. We’ll begin with Cercis canadensis, an understory tree commonly known as eastern redbud.

Eastern redbud is distributed across central and eastern North America, south of southern Michigan and into central Mexico. It is also commonly grown as an ornamental tree outside of its native range, and a number of cultivars have been developed for this purpose. Mature trees reach up to 30 feet and have short trunks with wide, rounded crowns. Its leaves are entire, round or heart-shaped, and turn golden-yellow in the fall. Gathered below the tree in winter, the leaves maintain their shape and are a light orange-brown color.

fallen leaf of eastern redbud (Cercis canadensis)

Eastern redbud is alternately branched with slender, zig-zagging twigs that are dark reddish-brown scattered with several tiny, light-colored lenticels. Older sections of branches are more grey in color. Leaf scars (the marks left on twigs after leaves fall) are a rounded triangle shape and slightly raised with thin ridges along each side. The top edge of the leaf scar is fringed, which I found impossible to see without magnification. Leaf buds are egg-shaped and 2-3 mm in length with wine-red bud scales that are glabrous (smooth) with slightly white, ciliate margins. Descriptions say there are actually two buds – one stalked and one sessile. If the second bud is there, it’s miniscule and obscured by the leaf scar. I haven’t actually been able to see one. Twigs lack a terminal bud or have a tiny subterminal bud that points off to one side. The pith of the twigs is rounded and pale pink. Use sharp pruners or a razor blade to cut the twig in half lengthwise to see it.

twig and buds of eastern redbud (Cercis canadensis)

Bark is helpful in identifying woody plants any time of year, but is especially worth looking at during the winter when branches have gone bare. The bark of young eastern redbud is grey with orange, furrowed streaks running lengthwise along the trunk. In mature trees, the bark is gray, scaly, and peels to reveal reddish-brown below.

bark of young eastern redbud (Cercis canadensis)

bark of mature eastern redbud (Cercis canadensis)

Eastern redbud is in the bean family (Fabaceae) and its flowers and fruits are characteristic of plants in this family. Fruits can persist on the tree throughout the winter and are another way to identify the tree during the off-season. Seed pods are flat, dark red- or orange-brown, and up to 2.5 inches long with four to ten seeds inside. The seeds are flat, round, about 5 millimeters long, and ranging in color from orange-brown to black.

persistent fruits of eastern redbud (Cercis canadensis)

seeds of eastern redbud (Cercis canadensis)

Eastern redbud flowers in early spring before it has leafed out. Clusters of bright pink flowers form on old branches rather than new stems and twigs. Sometimes flowers even burst right out of the main trunk. This unique trait is called cauliflory.

cauliflory on eastern redbud (Cercis canadensis)

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Photos of eastern redbud taken at Idaho Botanical Garden in Boise, Idaho.