Recently I enjoyed the winding trail in the floodplain at the Middle River Forest Area (Adair County), as it bent around obstacles; the trail would undulate up and down and side to side, and it was a fun walk on a beautiful afternoon. I practiced a little winter tree identification, admiring the trees and shrubs. I noticed many Ohio Buckeye (Aesculus glabra) trees growing, colorful in the late afternoon sun, and I started to examine them closely. I noticed that the trees varied in branching pattern, twig and trunk bark color and texture, size and shape of buds, and numerous other characteristics. All had the telltale opposite leaf arrangement and large shield-shaped leaf scars containing three bundle scars. Overall they surely looked like their species. And yet, they each also each looked distinctive and unique. Which of course, they are! Among other considerations, this is useful to keep in mind when using an identification guide. The classic Tree Finder book by Watts admonishes the reader to “avoid freaks.” I solemnly point this out to students when introducing the book, suggesting it as good life advice, perhaps to also apply in personal relationships? (I helpfully try to pass on my wisdom to the youth.)
But back to the Buckeye: as you might observe in this photo montage, they each look different, with a size and shape and spatial orientation all telling the story of that particular tree. The old argument of “nature or nurture” or “genes vs. environment” is tiresome, and frankly, wrong-headed. Let me settle this once and for all: every organism is the product of genetics and environmental conditions interacting. It is never one OR the other; it is always AND. So, these trees grow that way, in that spot, because of the story of their lives. Those exact same seeds planted someplace else, or in the same spot a different year, would result in a tree that looked different. Trees are born with a genetic toolbox and start life inside a seed, with a lunch packed by Mom. After that, they are constantly growing, and their growth makes the best of the situation in which they find themselves.
Buckeyes and other plants in wetlands also tell another story: the story of wetland hydrology. Among the growth conditions to face is flooding. All plants need water of course, but too much water can “drown” the plant: every cell in the plant need oxygen, and generally that oxygen comes from the air…and submersion in water makes that unavailable.The plant may have the ability to “hold its breath” for a while, but eventually the physiological constraints will be too much. Unless of course, you are a hydrophyte, specially-adapted to grow in flooded conditions. Then it becomes a question of how deep can the flooding be, and flooded for how long, before it is too much.
As described by Ralph Tiner in a classic article, the hydrophyte concept is useful in wetland determination. We have a list, now available as part of the on-line PLANTS database, and the so-called Indicator Status tells us the probability that we are in a wetland if we see a certain plant species. An OBL plant is OBLigated to grow in wetlands (99% probability), an UPLand species less than 1% chance, and so forth. And our Buckeye friend? It is FACultative—implies equal chance wetland, or not.
But, as pointed out in Tiner’s article, it may not be so simple. In fact, FAC plants are species that may very well be wetland-tolerant, in some cases. Within a species, certain genetic types, populations, or individuals may be well-adapted for wetlands, and they are ecologically hydrophytes, even if the species overall doesn’t have a narrow tolerance. Tiner recommends looking more closely at species with broad tolerance to wetland conditions, to see if we can identify the true wetland plants with more specificity. Some individuals will not only appear different, but will have different tolerance to flood conditions. My colleagues elsewhere have started to take up this challenge. But in the meantime, we should look beyond hydrophytes for a variety of indicators of wetland conditions.
And we should be aware and accepting of all our Buckeye trees. Here in Iowa, I see them mostly in valleys, and I have often noted those habitats as floodplain wetland sites. Perhaps our hotter, dryer summers restrict them to lower, wetter areas compared to typical Ohio populations? Perhaps we happen to be on the edge of the species’ range, and out here on the fringe, interesting genetic differences arise? In any case, the Buckeye trees at Middle River, and their river-edge comrades (Boxelder, Acer negundo, or Bladdernut, Staphylea trifolia) all grow beneath the canopy of Iowa’s favorite floodplain species, Silver Maple (Acer saccharinum). And every one…is an individual.