Tuesday, April 9, 2013

Nature Notes from Steve Young: Club Mosses

            About half a billion years ago, plants began to colonize the land. For the first few million years, none were more than a few inches tall, since, like today’s mosses, their bodies contained no conductive tissue. There was no way to lift water from the ground to leaves or to return nutrients to cells beneath the ground, where no sunlight could reach and allow photosynthesis. Once the interior plumbing of the vascular system evolved, the sky was the limit. Gigantic, primitive, spore-bearing trees covered much of the earth by the time the first land vertebrates laid their soft, vulnerable eggs in the coal swamps, long before the earliest dinosaurs walked the earth.

            Very early in their history, the vascular plants split into two groups. One of these has been wildly successful and now includes all the seed plants—flowering plants and conifers and their relatives, as well as ferns and horsetails. The second group flourished in the far distant past, but is now represented only by a few plants that are, in many respects, living fossils. The most conspicuous of these is the clubmosses. These have traditionally been considered to belong to a single genus, Lycopodium. (Modern authors have split it into several groups, but we needn’t bother with this here.) Lycopodium translates as wolf’s foot, and one of our commonest species is L. clavatum, wolf’s claw
clubmoss. (Clavatum means ‘with a club,’ referring to the club-shaped spore bearing organs that give clubmosses their common name. It should be said immediately that clubmoss is a misnomer; true mosses are non-vascular plants.
            There is probably no better place in the world to become familiar with clubmosses than here in northern Vermont. Although they are low-growing and relegated to the forest floor, they can dominate this layer, forming a sheet of evergreen cover that may extend over large areas. A fine example of this is at the Barr Hill Nature Preserve in Greensboro, where L. annotinum—shining clubmoss—makes a thick, continuous blanket under the spruce groves. But similar situations are widespread, and other forest types have their own, often somewhat less conspicuous, species. In fact it is possible to find eight to ten species within our area, the exact number depending on which botanist’s classification system is used. Most of the species are extremely widespread over the earth. I found colonies of L. clavatum on Kerguelen Island, which lies south of the Indian Ocean and over 1,000 miles from the nearest continent—Antarctica! Many of our species can be found in Alaska, Europe, or Siberia, but I’ve never seen them growing as richly and conspicuously as they do here in Vermont.
            Clubmosses are spore-bearing plants, and the spores germinate into tiny, inconspicuous plantlets called gametophytes, which even most botanists have never seen in the wild. The gametophytes may live for many years, ultimately producing eggs and sperms, whose union results in tiny new green embryos, which slowly grow and spread to form the familiar colonies of our forests and old pastures. These colonies are really single plants, very extensive and, presumably, very old, although I know of no data on just how many decades—or centuries—have elapsed since their beginnings.
            Among the best things about clubmosses is that they are abundant, are relatively easy to identify, and the presence of individual species is often associated with a particular habitat type, so it’s easy to predict which may be found where. There are also some relatively uncommon species, and it’s always exciting to come upon one, or to learn exactly what ecological settings in which to look for them. One of our species, L. inundatum—bog clubmoss—is best sought on the surface of the sterile soil of scraped road cuts a few years after the bulldozer has been through. Look for it where you see the sticky tentacles of sundew leaves and the September flowers of ladies’ tresses orchid—I’ve never found it in a bog.
            Clubmosses are traditionally, and incorrectly, often called fern allies, and a good book for learning how to identify them is the Peterson Field Guide to the Ferns. The pen and ink drawings by Laura Louise Foster are both botanically impeccable and artistically exquisite.

Steve Young

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