Vitaceae Seedlings; A Mystery No More

Sampling plants in quadrats is a challenging endeavor. It requires a taste for botany in its most raw and primitive state. Plants encountered in quadrats are almost always sterile and range from newborn seedlings to the withered remains of plants that may have senesced earlier in the year; and everything green in between. The field botanist spends countless hours in a growing season on his knees, head buried in vegetation, straining to use a hand lens at ground level in order to examine such subtleties as the red calluses on the teeth of Ceanothus americanus seedlings or the length of the ligule that separates Andropogon virginicus from Andropogon scoparius (Schizachyrium lacks taxonomic credibility when applied to Little Bluestem).
All this with the discomfort and sometimes fear that ticks, chiggers, horseflies, deerflies, yellow jackets, mosquitoes, gnats, spiders, snakes, falling limbs, storms, poison-ivy, heat and meth-heads illicit all around you. You know you have reached the pinnacle of a seasoned field botanist when you choose to examine a deftly teased Scleria achene between your fingers before you tend to the thousands of seed ticks that have just colonized your hand, or to wipe the searing sweat from your burning eye sockets.

In spite of this, the forests, woodlands, glades and prairies are our laboratories, where we test and untangle the differences in taxa by their simplest organs; their leaves and stems. Hard won are the tricks of our trade and they evoke an excitement that can be shared with few and appreciated by even fewer. After 12 years in the field, I am still a student of the flora and each day I am humbled by the myriad challenges of the trade.

I write this as a prerequisite for the information below in the hope that it will put the breadth of these findings into perspective. For each season a few new mysteries are solved; the knowledge that the Vaccinium can be distinguished by their venation patterns, that Impatiens can be discerned by the number of teeth on the leaf margins, that species in the genus Aristida actually have solid vegetative characters. This is the gold you can never mine from “the literature”. Sadly, it has no outlet.

One of the great unsolved mysteries in vegetative sampling has always been how to distinguish the cotyledons of Parthenocissus quinquefolia (Virginia Creeper) from Vitis aestivalis (Summer Grape). Both are members of Vitaceae (the grape family), both are commonly encountered and both germinate and persist throughout the summer. In the past, when these little groaners were encountered, they were entered onto the datasheet as “Vitaceae”; a moniker that lacks ecological significance and provides no information other than simple occurrence. This has all changed.

Earlier this summer I was innocently sampling a plot when what should appear within the boundaries of my quadrat but a bushel of Vitaceae seedlings. The first one I glanced at had three leaflets on the first true leaf emerging from between the cotyledons thus instantly giving it away as Parthenocissus. The next had one distinct leaf of a Vitis aestivalis. As I surveyed the quadrat and surrounding area I realized I was in an ocean of both species all with cotyledons intact and with one corresponding true leaf. Perhaps the tree above, lacking vines of either species, had been a turkey roost or an opossum hangout. Regardless, the area was strewn with an incredible density of both species in seedling form. I told myself that this was an opportunity not to be missed.

After a half hour of examining everything from stem thickness to overall color, I could find nothing consistent to differentiate these two beast and I had all but decided that my little observational study was as it had been, inconclusive. Then I noticed the broadly truncate-ovate bases of the Parthenocissus cotyledons and how the cotyledons were about as long as broad and thus rather deltoid in outline.

Comparing a Vitis seedling, I found the cotyledons of Vitis to be more rounded at the base and cleanly ovate in outline (longer than broad but broadest below the middle).

Twenty or thirty seedlings later, I was consistently and accurately using these characters to distinguish the two. I collected and pressed several examples and went about my merry way. For the remainder of the summer, as I have hiked to plots or walked between quadrats all over the Ozarks, I have kept an eye out for more seedlings and have found these characters to hold with 100 percent consistency. In fact, I don’t even pause anymore. They are so distinct that now I can’t imagine how this difference has gone undetected for so long.

Though this may seem insignificant in the grand scheme of nature and its study and though these findings will never grace the pages of Science, I smile every time I think of the simple hidden beauty that eluded field botanists for so long. Discoveries like this fuel my hope that some day field characters for such notorious complexes as Zizia aurea/Thaspium trifoliatum and Liatris aspera/scariosa/squarrulosa will seem as obvious as the vegetative differences between Impatiens capensis and I. pallida. The more we learn, the cleaner the data we collect. The cleaner the data, the better the management decisions based on these data will be. To me, this is science at its best; ever learning, ever revising and always hashing out the details regardless of the annoying gnat in your eye, the itch of poison ivy or the hundreds of chiggers slowly digesting the flesh from around your ankles. Afterall, science is stone.

Comments

  1. Cool post. How can you tell the Impatiens apart by their leaf margins?

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  2. Nice work, Justin. While you state "I can’t imagine how this difference has gone undetected for so long," it is obvious to me... only a handful of us are taking the time to look so closely, to spend the summer on our hands and knees, amongst the Lilliputian cotyledons. Too many times, I've heard from those who sample quadrats that they don't acknowledge anything under a certain height. Even many of those who spend the time trying to account for every plant in a quadrat don't spend what I consider to be enough time wading through the grasses and sedges to see the seedlings. And, as I've said before, there are even fewer who have the innate ability that you do to find and describe these differences. I certainly don't have it. I can often see that there is a difference, as small as it may be, but putting that difference into hard characters is another story.

    I congratulate you on this monumental discovery!

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  3. Ben-

    I was saving this topic for a future post, but seeing how free and open communication is the foundation of science, here it is.

    To distinguish the Impatiens, carefully follow these stemps: 1.) Pick a large leaf from the plant. 2.) hold the leaf up to the light as though it were a stained glass window. 3.)close one eye, preferably your non-dominant eye. 4.) Now slowly count the number of teeth on the left or right margin (ignoring the terminal tooth).

    If there are 9 or more teeth per side, you have I. pallida. If there are 9 or fewer teeth per side, you have I. capensis. Overlap in tooth number (nine teeth) occurs in about seven percent of leaves (based on approximately 200 specimens from throughout the range of each species). In which case use the average number of teeth on several leaves. Amazingly, when you have done this once you will realize that I. pallida is just toothier with teeth having about equal rise as run and that I. capensis has widely spaced teeth with more run than rise. Oh yeah, and feel free to skip steps 1 through 3.

    Scott-
    I know for a fact that you are a quadrat sampling machine and undoubtely have the requisite eye and abstraction of mind to communicate the subtilties of your craft.

    There really needs to be a published outlet for the identification characters devised by field botanists. Otherwise, our hard won discoveries will remain in obscurity until they are entombed beside the nearly deceased field of organismal biology. Such an arena would also serve to promote the idea that it can actually be done. To many time have I, and I'm sure you, been told that there is no way to distiguish the Asters or Sedges vegetatively. Granted, this should in no way replace taxonomy, but bridge the gap between those performing academic taxonomy and those attempting to identify plants in situ.

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  4. Perhaps the most trivial point in your post, but can you elaborate on this statement, "...the length of the ligule that separates Andropogon virginicus from Andropogon scoparius (Schizachyrium lacks taxonomic credibility when applied to Little Bluestem)." This entomologist is having a whale of a time trying to keep these grasses straight.
    regards--ted

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  5. Hi Ted,

    Gladly! The ligule of A. scoparius ranges between 1.0 and 2.0mm in length, while the ligule of A. virginicus is always less than 1mm long (usually around 0.5mm long).

    Finding a ligule on these grasses can be a challenge until you get the feel for it. The best way is to yank a sterile stem (not bolting) from the clump. Both species have folded leaf blades and sheaths so the sterile stems are very flattened. Next, isolate a leaf and sheath and follow the blade down until you see a discolored spot where the sheath and blade joint. At this spot, unfold the leaf blade and you will see the membranaceous ligule hidden within. Or you can pinch the sheath just below this spot and tear the blade from the top of the sheath. The ligule will remain attached and will be jutting out opposite the tear.

    As for the Schizachyrium comment: The paper that sank Andropogon scoparius into the genus Schizachyrium (Gould, F. W. 1967. The grass genus Andropogon in the United States. Brittonia 19(1): 68–73) is based on very arbitrary characters. Basically, Gould proposed that all Andropogon that have single spikes (as opposed to paired spikes as in A. virginicus) should be a different genus even though the spikes themselves are nearly indistinguishable morphologically. Anyway, I'm not convinced the change was taxonomically meaningful or useful so I still refer to the entity as A. scoparius.

    Thanks for your interest. Justin

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