8 Fabaceae (Pea Family)

Feeding the Soil

Day two of the tree labeling project arrives with the same beautiful weather as the first. In Minnesota, weather is the first thing one usually notices and shares as part of the morning routine. After groggily establishing what the day is like outside, I grab my gear and make my way over to the meeting place Susan Jane and I have settled on for this morning. I pull into the Lakeside Pavilion parking lot, turn off the car, and settle in to wait for her arrival. Knowing that 38 trees will all be tagged by the end of today fills me with both incentive and enthusiasm. More than half of these are additional species to the original self-guided map. Gratefulness washes through me at being able to share my love of trees with people in this manner and also through leading the in-person park tree treks. I take a sip from my water bottle, lean back in the seat, and close my still sleepy eyes.

Just like yesterday beneath the eastern white pine, my mind drifts back again to the day of my first tree trek. It took place on a Saturday in late June. The day had unfolded warmly, temperatures in the upper 70s (hot in the sun) with a low dew point. It was the kind of perfect summer day we dream of during the winter. The night before, I had hardly slept out of sheer nervousness. Even though I had prepped for the event extensively, that doesn’t always help to calm anxiety or to induce sleep. Having never led an outdoor talk before, I didn’t know what to expect. My experience giving presentations to school and library programs, however, sharing my art process illustrating children’s picture books did provide me with an invaluable foundation, not to be discounted. One thing leads often to the other in life, even if you have no idea how or where that future will happen!

When morning arrived at last, I felt much better getting ready, up and moving about. By the time I was dressed and pinning on my Naturalist ID tag, I felt calm (enough) and full of anticipation. The moment for carrying on my dad’s legacy had arrived! It was a reality. This thought lifted me up considerably. Going over my detailed tree notes one more time, I had a sudden image of all those trees in the park waiting for me, and I spoke aloud my sudden realization as if hearing my dad’s voice telling me, the way he would talk to me,

“You’re among friends!”

Yes! I am. I feel support, energy and love coming from trees, and this thought calmed me as I drove to the same parking lot where I’m waiting today; the same way it calms me now as I reminisce. When people started arriving, two of my dad’s ski friends showed up, a couple well-known to me. What a nice surprise! Then a very close friend of mine joined the group as well. I soon came to understand that everyone who had signed up for Tree Trek had some sort of positive connection with trees, and therefore, were just as interested in being here as I was. The truth is, many friends surrounded me!

We started off beneath the honey locust tree (Gleditsia triacanthos). The delicate leaves of this tree fluttered merrily above us as we gathered below in their comfortable shade. Honey locust leaves are described in botany as twice compound, pinnate. Another way to say it is that they are bipinnately compound. This type of leaf arrangement presents small leaflets growing up either side of a central stem, sort of like a fern. The tip of the honey locust leaf ends in two opposite leaflets on either side with usually no leaf tip coming out the center. In contrast, its cousin the black locust (Robinia pseudoacacia), typically sends a single leaflet out the tip. This is an especially useful way to distinguish between the two, say, for example, if locust sprouts appear in the spring in the yard of the new house you just purchased. No flowers, no fruit, and both types of trees around in the neighborhood. How would you know? So, there’s a way to be able to distinguish honey locust, which is edible, from its mostly toxic look-alike cousin, black locust. Fair to say that would be important to know.

The fossil record shows that both these tree species date back to the Early Pleistocene epoch. The Park locusts are mostly thornless varieties, but originally both species had thorns up and down their branches and trunks, theorized to give protection against large bite-taking mammoths and other mammals of the Ice Age.

Honey locust and black locust both belong to the pea family, the same family in which all legumes are classified, Fabaceae. Like beans or peas, they fix nitrogen in the soil where they grow, especially if they find themselves growing in nutrient poor soil. When that happens, nodules on their roots that contain bacteria can ‘fix’ nitrogen from the air into an organic form the bacteria can use. The tree gets nitrogen, and the bacteria get carbon and a safe place to live. What an amazing discovery to me when I first learned this fact! I never imagined that a tree could be a legume. Black locust, however, is toxic in all parts except for the lovely, white flowers which bloom about the same time as the honey locust flowers do. Their flowers have a subtle, indescribable taste of their own; pick of few to try when the blossoms are still freshly crisp. Black locust flowers are luscious and exotic sprinkled on salads or batter fried into little flower fritters. The rest of the plant is potentially fatal to animals and humans. So, don’t eat black locust pods or any other part of the tree!

Honey locust, on the other hand, is so-named for the sweet pulp lining the fully matured seed pods. As with any wild edible, some people are sensitive and may experience some unpleasant side effects, while others are not. So, proceed slowly at your risk and with caution. For millennia, however, humans have survived wild foraging, scraping out and enjoying the bounty nature provides around us including the sweet pulp of honey locust pods.  Also edible are the young pods when they are unripe and tender. As for the honey locust flowers, well, just don’t eat those!

Come fall, distinguishing these two trees is very easy by observing their fruit. Black locust pods are only about 3 to 4 inches long, straight, brownish-tan at maturity and thin. Honey locust pods, on the other hand, hang in long, wide twists up to 15 inch long with plump, shiny seeds inside. When mature, the pods are a deep, rich brownish purple. Telling them apart by their leaflet shape is a bit trickier, both being roundish with no pointed tip. Still, if you look closely, honey locust leaves are more oval compared to those of the round-shaped black locust leaves. In addition, black locust leaves are always singly compound, not twice compound (as mentioned) like honey locust. Honey locust trees are quite prevalent in the park, which is a good thing because black locust is considered invasive in Minnesota. Honey locusts, on the other hand, are native to Minnesota (at least in the southeastern corner), and thus make a natural choice for lining the streets in the park. Come autumn, their dainty yellow leaves carpet the area beneath creating an engaging musical swish-through experience a bit different compared to the ruffle-through sounds of most deciduous leaves. Maybe analogous to drums vs. the triangle in the percussion section? Just an idea.

And that was the honey locust!

Making our way up the gentle slope to our next stop, I gestured toward the top of the hill where the trees native to the Rockies and westward grow. I joked,

“Does it feel a bit cooler to you now?” as we climbed. “We’re heading up into the mountains!”

A woman traversing the grass next to me made friendly conversation along the way.

“I worked with your dad on the environmental committee,” she said, “And I remember your daughter attended at least one of his early tree treks.”

“Really? She never told me that!”

Another surprise revelation! I’ve since learned from my daughter that Grandpa took her on many such adventure walks and rambles through the park. She is a geologist now is the person who computer-generated the printable map of the tagged tree locations you can find at the beginning of this book — her contribution to the project of expanding her grandpas original tree tag map. She has her own memories and tree stories that hold roots of meaning for her reaching way back. In fact, she told me later,

“Grandpa and I talked a lot about trees. I loved those times with him. Grandpa showed me what buckthorn was, and honey locust. I always thought locust was a funny name for a tree!”

My thought exactly!

The woman walking next to me introduced herself as Susan Jane. Throughout the walking tour of trees, she asked good questions or made relevant comments at almost every stop. She seemed very interested and knowledgeable, and this impressed me.

As planned, our first tree of the Rockies on top of the hill was the Douglas-fir, then the white fir and ponderosa tagged trees. Traversing from there past the labyrinth area to what I call the Ohio Buckeye Valley, we made a quick stop at the ironwood tree and the Northern catalpa growing nearby.

Still sitting and resting in the car, my thoughts land pleasantly upon each of these trees to which I led people on that first Tree Trek, and they soon branch into a myriad of connections, like roots and synapses sparking memories, conversations, and interactions that can feed an entire human lifetime.

The lovely, white flowers of the Northern catalpa (Catalpa speciosa) blanketing its branches in June, a tropical species in the family Bignoniaceae that grows in temperate regions. How the petals present their own purple speckled landing pad complete with two, fuzzy yellow beacons guiding the way in for arriving insects. My dad sharing his enthusiasm over discovering this gorgeous flower in the park and sharing a photo with me which I now use as a reference. How in the fall, the 10-20 inch long cigar-like, slender pods hang down in a vivid exhibition of this tree’s seed production method.

The pretty nutlet clusters of the ironwood tree (Ostrya virginiana) decoratively ornamenting this understory shrub of the upland forests (sugar maple-basswood), a sight that fills me with gladness, reminds me of the oaks, evergreens, ferns and wildflowers that grow alongside them, and how the nutlets sustain squirrels, mice and a huge variety of birds.

Seeing in my mind’s eye the Ohio buckeye (Aesculus glabra) that was growing in the yard when we bought our house, my first introduction (having never seen or noticed one before). My dad becoming very interested in my identification of this tree, for it was new to him as well. Explaining to the group that its fruit is not a true nut, although it resembles a chestnut, but is rather a seed with a hull. People sometimes carry them in their pockets for good luck. The horse chestnut (Aesculus hippocastanum), its cousin, is not really a chestnut (or a true nut) either, that both trees belong to the family of Soapberry (Sapindaceae). The memory of our large buckeye tree broken in half after a summer windstorm one year, crashing over the neighbor’s driveway. How we left the stump there, now an attractive shrub of buckeye suckers continuing to provide a living screen from the neighboring yard, and gloriously alive in springtime with buzzing bees pollinating their flower clusters. How every one of those seeds formed from the flowers a squirrel will claim, bury, eat and otherwise make off with, for they love those ‘nuts’! How they are toxic to humans. How, in winter, buckeye leaf scars beam out, each face with a slightly different smile and variation especially on younger sprouts with their particularly large buds. The portrait gallery of photos I made one year of buckeye leaf scar faces.

Trees truly give me joy.

Research studies have shown that walking among or just living near trees can benefit human health. In Japan, a meditative walk through a forest heals in the way known as shinrin-yoku translating as forest bathing. Forest researchers have uncovered a vast social network occurring among trees (hormonal, electrical signals, warnings of danger, shared nutrients, etc.) below ground in the vast network of their root systems. Depending on the species, important, symbiotic relationships develop into a vast, complex network within the soil between tree roots and the fungi that grows within or around them. Trees communicate. People have assumed that trees compete in an ongoing battle for nutrients, light, and water with the winner beating out the others in a battle of the survival of the fittest – leaving the loser back in the shade to wither and die. Some researchers are beginning to question such generalizing assumptions. The relationships within a mature forest are much more complex. Two trees planted or happening to grow right next to each other are not necessarily competing for resources, energy, sunlight, air space, growth. Scientists are now providing evidence that trees are communal, cooperative and interdependent.

Most of a tree’s roots grow less than 12 inches or so below the soil surface. In deeper soils, many trees will drop some sinker roots which serves to stabilize the tree, but the vast majority of fine roots stay shallow and spread away from the trunk 2-3 times the canopy’s radius. Quite a distance! All those roots are busy! Nitrogen-fixing among legumes is only one small way to bring in more nutrients, and that of course is only confined to Fabaceae (the pea family). Most trees on Earth, in general, use a remarkable method to further increase their water and nutrient uptake in a process that involves fungi living in the soil around their roots. This association between a root and a fungus working together to benefit both organisms through symbiosis is called a mycorrhiza. My dad’s work involved researching (and teaching) the physiology and interactions of host-parasite relations. So, his work concentrated not on mycorrhizal symbiosis, but rather on parasitism in his field of mycotoxicology.

There are so many aspects one can cover when talking about trees!

The purr of a car pulling into the parking lot and then a door shutting, brings me out of my reverie. I open my eyes to find Susan Jane newly arrived and making her way over to my van. I get out and, on second thought, pull open the sliding door and invite her to sit down for a while. Instead of just setting right off, I feel like talking, getting to know her a bit. She agrees and joins me in the open space of the side door.

“I didn’t sleep well last night,” I tell her, yawning and stretching. “In fact, I haven’t slept well for some time now!”

“Oh, I’ve been through that before. I feel for you,” she replies.

“Yes, I’m caregiving for my mother this week with the help of my husband. He joined me this time so he could keep her company while I do this project.”

“That’s so helpful,” says Susan Jane. “Be sure to thank him for me!”

For the next several minutes or so we plant the little garden of a new friendship, feeding it with our empathic talk. We talk about our mothers, our family dynamics and difficulties that formed our growth as children. What our adult sibling relationships are like now. What our dads were like.

“My dad had to have things his way,” I say.

“My dad was an absolute perfectionist!” she remarks in her turn.

And it feels good, knowing that we all come from somewhere; each childhood is filled with different circumstances and contexts that include the joy of roses and sunshine, but not always. Many things shape us both good and bad; all of us are fragile beings, searching, doing our best in living our lives to flourish, grow, and find happiness. We all need each other.

Time is moving on, though, and Kentucky coffeetree awaits.

“We should get going.”

We rise, hitch up our totes and gear, and set off to tag another leguminous tree in the pea family. Kentucky coffeetree (Gymnocladus dioicus) was so named by English speakers for its hard-coated, smooth seeds that these early settlers used as a coffee-substitute until the real thing became more widely available (which says much). One problem (besides the bitter taste) is that at least three hours of roasting is required to neutralize the toxic alkaloids. These trees date back to the Ice Age (like the locust trees) and were food for now extinct mammals that could chew and digest the hard seeds, as opposed to modern day ones who basically just avoid them. Without those ancient mammals to scarify the extremely hard seed coatings so that they can take up water and germinate, it is difficult for Kentucky coffeetree seeds to propagate naturally. This means most Kentucky coffeetrees in the wild expand themselves through root suckering. The problem here is that this leads to a monoclonal culture made up of just a few individuals and a limited gene pool. Luckily, their assets of attractiveness, hardiness and disease resistance do have rewards, for horticulturists continue to cultivate coffeetree seedlings in nurseries for planting on urban boulevards. Think about adding this tree if you have a place to plant one!

The Kentucky coffeetree we’re headed for lives just off the lower walking path going under the pedestrian bridge. At first glance, you might mistake its pinnate leaves as belonging to honey locust, especially since they are also twice compound. That again! But our coffeetree’s leaflets are longer with a little pointed tip on the end instead of rounded which helps a lot with identification. Knowing this, the other differences become clearer, such as the larger leaf size. Their fruits differ vastly as well.

The coffeetree we’re about to re-tag is a male who’s lost his sign. His mate is on our list as one of the new tagged trees because I wanted her attractive pods — wide, flat and leathery — to get some well-deserved attention. Inside are large, smooth seeds very uniform in size, attractively shiny. Deep brown when mature, the large pods feel good held in the palm, and are decorative hanging on the branches well into winter even after all her leaves have dropped. Our female tree lives on the other side of the pedestrian bridge beyond the Avenue of the Giants (as I call them), just up the hill from those huge specimens that date back to some of the original trees the park designers planted over 100 years ago. They are absolutely magnificent. She is a much younger tree than they, and is resplendently clad with clusters of gorgeous pods.

By now, Susan Jane and I have an easy pattern of approaching a tree and finding the best place to pound in its sign. After our recent, intense conversation sharing confidences, a burst of silliness comes over me. In front of the Kentucky coffeetree, I jokingly undulate my arms up and down as if to capture the tree’s vibrations or emanations.

“Feel the energy, ” I chant with eyes closed. “The tree will lead us to just the right spot.”

And it does. She laughs as we locate that place in a moment of shared camaraderie.

“It truly does take some evaluation,” she says.

She’s right, and every place we pick out together feels absolutely right.

“It’s nice to have someone to do this with,” I say, adding with a wink, “especially someone from the committee.”

“Of course,” she smiles in return, emanating an energy of her own into the lightness that has grown between us, one that feels just like the best part of what I receive from trees.


Tree Trek Copyright © 2022 by Stephanie Mirocha Ellison. All Rights Reserved.

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