Thursday, August 27, 2009

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.

Tuesday, August 4, 2009

Lactuca....hirsuta?

Lactuca hirsuta is one of the most under detected species of vascular plants in the Midwest. There I said it. It is completely off the radar for most folks, yet I see it with considerable frequency, at least here in the Ozarks. The USDA Plants website shows that it occurs in most every state northeast of Texas (north to MN and east to Maine and GA) yet it is listed from shockingly few counties in these states. I don’t know how this creature has escaped detection. Perhaps its anomalous distribution stems for the common precept that Lactuca canadensis can be distinguished from other Lactuca by the salmon/orange sap color. While this it true, one must then distinguish Lactuca hirsuta which also possesses this quality. This is easily done since L. hirsuta, as the name implies, is hirsute and L. canadensis is glabrous (disclaimer: some specimens of L. canadensis can be very slightly pubescent and some L. hirsuta can be sparsely pubescent but the vast majority are clear-cut).

Here is quick shot of the stem and leaves of L. hirsuta (above). And for comparison, here is a shot of the stem and leaves of L. canadensis (below). Also notice the difference in overall leaf shape between the two species.

There are other subtle but taxonomically satisfying characters. Most notably, the leaves of L. hirsuta are progressively shorter toward the top of the stem while those of L. canadensis remain roughly the same length from tip to toe. Also, the involucres of L. hirsuta are range from 15-22mm long where those of L. canadensis are typically 10-14mm long.

Lactuca hirsuta (above)
Lactuca canadensis (below); my thumb nail is 15mm long, for scale.

Esteemed Missouri botanist Alan Brant pointed out to me that the inflorescence (branches and involucres) of L. hirsuta are often infused with a dark purple coloration while those of L. canadensis are mostly green with some hits of purple here and there. That can clearly be seen in the involucre photos above.

So, as Lactuca are bolting and blooming across eastern North American, in your travels, keep an eye out for the lonely but hairy L. hirsuta. While I don’t have a great grasp on its habitat requirements (perhaps a bit more conservative than L. canadensis), it seems to prefer dry acidic soils with just a touch of disturbance suffused with a sparkle of full sun. Rocky soils with sparse vegetation that have recently witness fire are ideal. I remember seeing it at Indiana Dunes National Lakeshore. I can imagine that open sand would suit it just fine. Another place to find it would be the neglected stacks of almost any herbarium in eastern North America, where it has undoubtedly been misidentified as L. canadensis. Hey, let’s print off some annotation labels and head to the herbarium!