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.

Weeds of Boise: Northwest Corner of Ann Morrison Park

The Boise River, which winds its way through the City of Boise, is flanked by a series of parks known collectively as the Ribbon of Jewels, named in honor of prominent women in the community. Most of these parks are vast expanses of turfgrass scattered with large trees and are meticulously maintained, except near the river where the vegetation is allowed to run a little wild. It is within these narrow strips of land, bordered on one side by the river and the other by regularly mowed turfgrass, that a veritable nature walk can be had right in the heart of the city.

While a few native plant species can be found in these strips, much of the vegetation is introduced. Some of the non-native trees and shrubs may have been intentionally planted, while others came in on their own. Most of the grasses and forbs in the understory are weedy plants commonly seen on all manner of disturbed lands. There are also, of course, a few weeds specific to riparian areas. Due to the wild nature of these strips and the abundance of introduced plants, the river’s edge makes for a great place to become acquainted with our wild urban flora.

Looking at the northwest corner of Ann Morrison Park from the Americana Boulevard Bridge

Because these parks (which include the Boise River Greenbelt) stretch for miles through the city, practically any spot along the way could be a good place to look for weeds. I chose to narrow my search to the northwest corner of Ann Morrison Park. What follows are a few images of some of the plants I found there, along with a list of what I was able to identify during my brief visits this spring. The list will surely grow as I check back from time to time. If you’re interested in learning more about the Boise River and its importance – not just to the humans who call Boise home, but also to myriad other living organisms – check out Boise River Enhancement Network and the work that they are doing to help protect and preserve this invaluable ecosystem.

yellow flag iris (Iris pseudacorus)

Russian olive (Elaeagnus angustifolia)

common mullein (Verbascum thapsus)

climbing nightshade (Solanum dulcamara)

cleavers (Galium aparine)

a strip of cheatgrass (Bromus tectorum)

seed head of dandelion (Taraxacum officinale)

western salsify (Tragopogon dubius)

bull thistle (Cirsium vulgare)

Amur honeysuckle (Lonicera maackii)

creeping buttercup (Ranunculus repens)

Weeds found at the northwest corner of Ann Morrison Park (while several of the trees and shrubs at this location are introduced, I only included those species that are generally considered to be weedy or invasive):

  • Amorpha fruticosa (false indigo bush)
  • Anthriscus caucalis (bur chervil)
  • Arctium minus (common burdock)
  • Bromus tectorum (cheatgrass)
  • Capsella bursa-pastoris (shepherd’s purse)
  • Cerastium vulgatum (mouse-ear chickweed)
  • Cirsium arvense (creeping thistle)
  • Cirsium vulgare (bull thistle)
  • Chondrilla juncea (rush skeletonweed)
  • Convolvulus arvensis (field bindweed)
  • Conyza canadensis (horseweed)
  • Descurainia sophia (flixweed)
  • Elaeagnus angustifolia (Russian olive)
  • Erodium cicutarium (redstem filaree)
  • Euonymus fortunei (winter creeper)
  • Galium aparine (cleavers)
  • Hordeum murinum ssp. glaucum (smooth barley)
  • Iris pseudacorus (yellow flag iris)
  • Lactuca serriola (prickly lettuce)
  • Lamium amplexicaule (henbit)
  • Lonicera maackii (Amur honeysuckle)
  • Malva neglecta (common mallow)
  • Medicago lupulina (black medic)
  • Parthenocissus quinquefolia (Virginia creeper)
  • Plantago sp. (plantain)
  • Poa bulbosa (bulbous bluegrass)
  • Polygonum aviculare (prostrate knotweed)
  • Ranunculus repens (creeping buttercup)
  • Rumex crispus (curly dock)
  • Sisymbrium altissimum (tumble mustard)
  • Solanum dulcamara (climbing nightshade)
  • Sonchus sp. (annual sow thistle)
  • Taraxacum officinale (dandelion)
  • Tragopogon dubius (salsify)
  • Trifolium repens (white clover)
  • Ulmus pumila (Siberian elm)
  • Verbascum thapsus (common mullein)

Like all posts in the Weeds of Boise series, this will be updated as I identify and photograph more of the weeds found in this location.

Vines for Spring

I’m taking a break from writing a regular post this time around. It’s the first week of spring, and there is a lot going on. I hope you are getting outside and enjoying the warmer weather (at least those of you in the northern hemisphere anyway). It was a pretty mild winter in my neck of the woods, but that doesn’t diminish my excitement when I see plants start to flower and leaf out. The gray days of winter are largely behind us, and holing up in my cave of an apartment is suddenly less appealing.

What I have for you this week are some short video clips. I recently joined Vine, a short-form, video-sharing social media site where each post is a six second, looped video. I’m late to the scene as usual, but I’ve been having fun messing around with it. The following videos are some of my first attempts (and lousy ones at that); if I decide to stick with it you can expect better content. If you’re interested in this sort of thing, please join, follow, favorite, share, like, comment, etc. Regardless, I hope you will find time to pry yourself away from a screen and experience nature during this beautiful and singular time of year.

 

 

 

 

Awkward Botany is also on Twitter and Tumblr, so feel free to follow me there too if you would like. Happy Spring!