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

More Winter Trees and Shrubs:

Vacant Lots as Habitat for Insects

Urban areas are increasingly being studied for their potential to help conserve biodiversity and provide habitat for numerous plants and animals. Despite the harsh conditions of the built environment, organisms of all kinds are able to survive in our cities, and as we find ways to make these spaces more hospitable for them, cities actually have great potential for species conservation, even for species that are rare, threatened, or specialized. One obvious way to accomplish this is to manage our yards, parks, and gardens as habitat, such as planting flower strips for pollinators. Another way, perhaps overlooked at times, is to manage and maintain vacant lots as habitat. Every urban area has some degree of vacant land that for one reason or another has not been developed, or that once was developed but has since been bulldozed or abandoned. Spontaneous vegetation quickly moves in to occupy these sites, and while some may see them as eyesores, their potential for providing habitat for an untold number of plants and animals is substantial.

In cities that are growing – like Boise, Idaho – vacant and abandoned lots are disappearing quickly as development strives to keep up with population growth. My first Weeds of Boise post took place at an abandoned Pizza Hut, which has since been demolished and is now the future site of a large building (see photo below). This is happening all over the city – the City of Trees is looking more like the City of Cranes these days. On the other hand, cities that are shrinking due to economic downturn, loss of industry, and other factors, have an increasing number of vacant lots, which offers the opportunity not only to maintain these lots as habitat, but also to carry out research that will help us understand how these locations can be best managed for species conservation.

Abandoned Pizza Hut Lot Now Under Construction

Cleveland, Ohio is one example of a “shrinking city.” Due to significant population decline, Cleveland has a growing number of vacant lots, many of which are maintained by the City of Cleveland Land Bank. For researchers at The Ohio State University, all of this vacant land presents an opportunity to study, among other things, urban biodiversity. Hence, the Cleveland Pocket Prairie Project was born. By assigning different management treatments to groups of vacant lots and observing the differences between each treatment, researchers can help determine the best strategies for managing vacant lots, particularly when it comes to biological conservation. One of the major focuses of the Cleveland Pocket Prairie Project is to determine how vacant land can provide habitat for insects and other arthropods.

In a study published in Sustainability (2018), researchers in Cleveland compared the species richness and abundance of bees found on vacant lots to those found on urban farms. Bee collections were made three times a year over a three year period. Of the more 2733 bees collected, researchers identified 98 total species representing 5 different families. The vast majority of the species were native to the area. Significantly more bees were found in vacant lots compared to urban farms. In both vacant lots and urban farms, the total number of ground nesting bees decreased as the proportion of impervious surfaces near the study sites increased. Plants that received the most bee visits on the urban farms during the study period were common milkweed (Asclepias syriaca), chives (Allium schoenoprasum), and squash (Cucurbita pepo); while the top three plants with the most bee visits on vacant lots were red clover (Trifolium pratense), white clover (Trifolium repens), and Queen Anne’s lace (Daucus carota).

ground nesting bee (photo credit: Sierra Laverty)

Bee communities differed between vacant lots and urban farms: 29 of the 98 total species were seen only in vacant lots, while 14 species were seen only at urban farms. Most of the bees collected in this study were ground nesting species, and researchers suspect the reason more bees were found on vacant lots compared to urban farms is that farms experience frequent soil disturbance in the form of tillage, weeding, mulching, and irrigation, while vacant lots generally do not. The researchers conclude that their study “adds to the growing body of literature advocating for the maintenance of minimally-managed vacant lot habitats as a conservation resource.” Vacant land that is “surrounded locally by high concentrations of impervious surface,” however, may not be the most suitable location to carry out conservation efforts.

In a study published in Urban Ecosystems (2020), researchers in Cleveland looked at the species richness and abundance of lady beetles in vacant lots. They were particularly interested in the potential that vacant lots may have in providing habitat for lady beetles that are native to the region. The study consisted of 32 vacant lots, each assigned one of four habitat treatments: control (seeded with turfgrass and mowed monthly), meadow (seeded with turfgrass and mowed annually), low-diversity prairie (seeded with three species of prairie grasses and four species of native prairie forbs), and high-diversity prairie (seeded with three species of prairie grasses and sixteen species of native prairie forbs). The two prairie treatments were mown annually. The majority of the nearly 3000 lady beetles captured across all of the plots over a two-year study period were exotic (introduced) species. Sixteen species total were collected: four exotic and twelve native.

The researchers predicted that the lots seeded with prairie plants native to the region would support a higher abundance of native lady beetles than those composed of turfgrass, especially those that are frequently mown. Surprisingly, a similar abundance and species richness of both native and exotic lady beetles were found across all treatments. What appeared to be important for native lady beetle abundance were vegetation features like bloom abundance, height, and biomass. The surrounding environment also matters. As the researchers put it, “vacant lots embedded in landscapes dominated by impervious surface and with a high degree of habitat isolation were less suitable habitats” – a similar conclusion to that made in the bee study.

Brachiacantha ursina (photo credit: Wikimedia Commons / NY State IPM Program at Cornell University)

The most abundant native lady beetle collected in the study was the ursine spurleg lady beetle (Brachiacantha ursina). The larvae of this beetle “infiltrate the nests of Lasius ants,” which is “one of the most common genera of ants found in urban environments.” Researchers posit that the abundance of B. ursina reflects the habitat preferences of ants in the Lasius genus. Several species of lady beetles native to the region are experiencing significant population declines, and the researchers were disappointed to find that none of the most rare species were collected during their study period. However, it was promising to find that “pollen and nectar provided by both seeded native and naturally occurring weedy plants” appeared to be important food sources for native lady beetles.

Both studies indicate that vacant lots can be important locations for habitat conservation in urban areas, particularly when they are part of a larger collection of greenspaces. In combination with managing our yards, parks, and urban farms as quality habitat for plants and animals, conserving vacant lots that consist of diverse vegetation (both planted and spontaneous) can help support insect populations within our cities.

2022: Year in Review

It’s time to look back on 2022. But before we do that, I have to acknowledge that January 2023 marks Awkward Botany’s 10 year anniversary. This time ten years ago, I was drafting the introductory post to this blog. Obviously, a lot has happened since then, yet it still seems like yesterday somehow. And while I may not be posting with the frequency that I once was, I’m still at it, and I don’t plan on stopping any time soon. There is so much we have yet to cover. I feel like we’ve barely scratched the surface of what the world of plants has to offer. If you’d like to look back on what I’ve written about over the years, these Year in Review posts are a good place to start, which I’ve been posting each year since Awkward Botany turned one. Looking forward, expect more of the same, which if you’re into plants as much as me, should be enough to keep your attention. If you’re not into plants, I’m not sure why you’re here, but since you are, I hope that what I share might change your mind. Either way, here’s to another 10 years!

Awkward Botany Turns 10!

Perhaps the most eventful thing that happened in 2022, as far as the blog goes, was my appearance on Outdoor Idaho where I got to sing the praises of weeds and the role they play as members of our wild flora. You can expect the weeds talk to continue, especially since Western Society of Weed Science’s Annual Meeting is coming to Boise later this winter. Perhaps I’ll see you there! Oh, and speaking of annual meetings, Botany is coming to Boise this summer, so please feel free to say hello if you’re coming to town.

As per usual, I have a head full of ideas and plans for the upcoming year, and I am hopeful that it will be one of the best yet. But I will spare you from having to trudge through that whirlwind, and instead I’ll just say thank you for being here. Thanks for your comments, shares, follows, and the other ways you show your support. If you’d like to continue doing so, by all means, please do. If you’re new here and you’d like to start, all relevant links are in the link tree below. Happy 2023 everyone!

Awkward Botany Linktree

And now…

A Selection of Posts from 2022

Winter Trees and Shrubs

Book Reviews

Weeds of Boise

Eating Weeds

Randomly Selected Botanical Terms

Guest Posts