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)

More Winter Trees and Shrubs on Awkward Botany:

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

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.

Field Trip: Hoyt Arboretum and Leach Botanical Garden

Thanks to Sierra having a work-related conference to attend, I got the chance to tag along on a mid-July trip to Oregon. My mission while she was busy with her conference was to visit some gardens in Portland. What follows is a mini photo diary of my visits to Hoyt Arboretum and Leach Botanical Garden. Both are places I had never been to before. My visits may have been brief, but they were long enough to earn big thumbs up and a strong recommendation to pay them a visit.

Much of the Hoyt Arboretum is like walking through a dense forest. Here a Scots pine (Pinus sylvestris) marks a fork in the road. To the right is the White Pine Trail, and to the left is the Bristlecone Pine Trail.

Some of the trees are enormous. This western redcedar (Thuja plicata) is getting up there.

Looking up to admire the canopy was one of my favorite parts. Here I am below the canopy of a vine maple (Acer circinatum).

And now I am below the canopy of a tricolor beech (Fagus sylvatica ‘Tricolor’).

Thimbleberry (Rubus parviflorus) was abundant, and the fruits were at various stages of maturity.

There were a few flowers to look at as well. Bumblebees were all over this Douglas spirea (Spiraea douglasii). 

Ocean spray (Holodiscus discolor) was in its prime.

Leach Botanical Garden is considerably smaller than Hoyt Arboretum but is similarly wooded. There is a creek that runs through a small ravine with pathways winding up both sides and gardens to explore throughout.

In wooded areas like this, there are guaranteed to be ferns (and, of course, moss growing over the fern sign).

There were several fruiting shrubs, like this Japanese skimmia (Skimmia japonica).

And this Alaskan blueberry (Vaccininium ovalifolium, syn. V. alaskaense).

Wood sorrel (Oxalis spp.) was abundant and often attractively displayed.

I found this insect hotel in the upper section of the garden. Apparently some major developments are planned for this area. Learn more here.

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Have you visited any public gardens this summer? Leave your story and/or recommendation in the comment section below.

Weeds and Wildflowers of the Boise Foothills: June 2015

Boise, Idaho is a beautiful city for many reasons. One feature that makes it particularly attractive are the foothills that flank the city from the southeast to the northwest. The foothills are a transition zone to the mountains that lie to the northeast. Large sections of the foothills have been converted to housing, but much of the area remains as wide open space. There are around 150 miles of trails winding through the foothills that can be accessed from the Boise area. These trails are used frequently by hikers, mountain bikers, dog walkers, bird watchers, trail runners, and horseback riders. The foothills, along with so many other nearby attractions, explains why Boise is such an excellent city for those who love outdoor recreation.

boise foothills trail

I feel embarrassed to say that I had not yet made it into the foothills this year until about a couple weeks ago. I had intended to go for more frequent hikes this year, but life has been in the way. What I was especially curious to see was how the plant life in the foothills changes throughout the year. Because Boise is located in a high desert and receives very little precipitation (especially during the summer months), many of the local wildflowers show themselves in the spring when there is moisture in the soil, after which they wither up and go dormant for the rest of the year.

But there is still lots to see in June. However, it should be noted that when you are hiking in the foothills you must develop an appreciation for weeds, as many of the plants you will see are not native to this area and, in many cases, are in much greater abundance than the plants that are. Species brought in from Europe and Asia have become well established in the Boise Foothills, significantly altering the area’s ecology. One of the major changes has been wildfire frequency. Before weeds like cheatgrass – an annual, shallow-rooted grass imported from Europe – became so prolific in the area, fires were rare, slow moving, and isolated. The continuous, quick burning fuel source provided by dead cheatgrass heightens the risk of more frequent, faster moving, widespread fires, especially in the hot, dry summer months. This threatens plant species that are not adapted to frequent fires.

But this post isn’t about the ecology of the foothills. We can save that for another time. For now, I just wanted to share some of the plants I saw – both native and non-native – on my short walk through a very tiny corner of the Boise Foothills earlier this month.

The trail that I hiked is one of several trails in an area of the Boise Foothills called Hulls Gulch Reserve.

The trail that I hiked is one of several trails in an area of the Boise Foothills called Hulls Gulch Reserve.

 

Bachelor's Buttons (Centaurea cyanus) are native to Europe. They are a common cultivated flower and have escaped from yards into the foothills. They are quite attractive and popular among pollinators. Their flowers and stems are edible so perhaps we should all take to eating them.

Bachelor’s buttons (Centaurea cyanus) are native to Europe. They are a common cultivated flower and have escaped from yards into the foothills. They are quite attractive and popular among pollinators. Their flowers and stems are edible, so perhaps we should all take to eating them.

 

Silverleaf phacelia (Phacelia hastate) - a foothills native that is also a pollinator favorite.

Silverleaf phacelia (Phacelia hastata) – a foothills native and a pollinator favorite.

 

Pale evening primrose (Oenothera pallida) - a foothills native pollinated by nocturnal moths.

Pale evening primrose (Oenothera pallida) – a foothills native pollinated by nocturnal moths.

 

Medusahead (Taeniatherum caput-medusa) is an invasive annual grass from Eurasia. It has an ecological impact similar to cheatgrass (Bromus tectorum).

Medusahead (Taeniatherum caput-medusae) is an invasive annual grass from Eurasia. It has an ecological impact similar to cheatgrass (Bromus tectorum).

 

The fruits of nineleaf biscuitroot (Lomatium triternatum), a spring flowering plant in the carrot family (Apiaceae).

The fruits of nineleaf biscuitroot (Lomatium triternatum), a native spring wildflower in the carrot family (Apiaceae).

 

Fruits forming on antelope bitterbrush (Purshia tridentata), one of several shrubs native to the Boise Foothills.

Fruits forming on antelope bitterbrush (Purshia tridentata), one of several shrubs native to the Boise Foothills.

 

Rubber rabbitbrush (Ericameria nauseosa), a native shrub that flowers in late summer.

Rubber rabbitbrush (Ericameria nauseosa), a native shrub that flowers in late summer.

 

Lichens on the branch of basin big sagebrush (Artemisia tirdentata sbsp. tridentata) another common native shrub.

Lichens on the branches of basin big sagebrush (Artemisia tridentata subsp. tridentata), another common native shrub.

 

Tall tumblemustard (Sisymbrium altissimum) an introduced species and one of many tumbleweed species in the western states.

Tall tumblemustard (Sisymbrium altissimum) – an introduced species and one of many tumbleweed species in the western states.

 

Little spider atop the flowers of western yarrow (Achilea millefolium), a foothills native.

A little spider atop flowers of western yarrow (Achilea millefolium var. occidentalis), a foothills native.

Learn more about the Boise Foothills here and here.

Where have you been hiking lately?

Idaho State Flower

In 1931, the Idaho state legislature officially designated Philadelphus lewisii as the state flower of Idaho, several decades after it was originally selected by a committee of Boise women. Affectionately referred to as “syringa” by Idahoans, P. lewisii occurs from British Columbia down into northern California and across into Idaho and Montana. Its native habitats are the bases of rocky slopes, rocky crevices, and stream banks. It was among many plants collected during the Lewis and Clark Expedition (1804-1806) by Meriwether Lewis. Lewis collected two specimens while in north Idaho and eastern Montana – the first near the Clearwater River and the second near the Bitterroot River. The species was later described by Frederick Pursh and named after Meriwether Lewis. Another widely accepted common name for this species is Lewis’ mock orange.

P. lewisii is a deciduous shrub that reaches 6 to 10 feet tall. It has opposite leaves and white, four-petaled flowers that appear in clusters of 3 to 11 on lateral branches. Young branches have reddish-brown bark that eventually peels off to reveal gray bark as the branches age. Many flowers in the genus Philadelphus emit a scent similar to the blossoms of citrus plants and have a general appearance akin to orange blossoms, giving them their common name “mock orange.” The attractive flowers and their sweet aroma are reasons why many people look forward to these shrubs blooming each year. Additionally, Idahoans can be certain that when their beloved state flower is in bloom, summer is imminent.

Philadelphus lewisii

The leaves and bark of P. lewsii contain saponins and can be used to make soap when they are crushed and mixed with water. This quality also makes the plant fire-resistant. The branches and hollow stems of P. lewisii were used by Native Americans to make a variety of useful items including snowshoes, bows, arrows, and pipes. The common name “syringa” was derived from the greek word “syrinx” meaning “tube.” This helps explain why lilacs, an unrelated group of plants that also has hollow stems, was given the latin name Syringa.

Philadelphus is a genus in the Hydrangea family (Hydrangeaceae) that consists of at least 60 species found throughout North America into Central America and in various parts of Eurasia. All are shrubs – some growing to 20 feet tall while others only reach 3 feet at maturity. Most have deciduous leaves, but a few are evergreens. Many cultivars of Philadelphus have been developed by the horticulture industry and are commercially available. Cultivars are often selected for their compact growth habit, abundant and sometimes double flowers, and their strong, sweet aroma.

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Check out this article in Pacific Horticulture to learn more about the genus Philadelphus.