Friday, March 19, 2004
Biodiversity Corner: Smooth Rock Tripe
Henry David Thoreau
Name: The 30 North American species of Umbilicaria are all referred to as rock tripes or tripes de roches, and sometimes as navel lichens. The common names for the different species generally include an adjective describing the texture of the surface. For example, there are frosted rock tripes, also folded, fringed, blistered, and peppered. The smooth rock tripe has the very mammalian scientific name of Umbilicaria mammulata — and I can't help but think of Britney Umbilicaria Spears and Janet Mammulata Jackson — but this lichen lives a life of quiet dignity in the woods.
When and where seen: There is a lot of smooth rock tripe in the Conant Land and I have also seen it in the Towle Field woods and at Greenough. It is quite common and can be found year-round. It grows in colonies on rocks and seems to prefer the steeper surfaces of large boulders. You seldom see it on rocks in stone walls — it seems to favor rocks that have been undisturbed for a looong, looong time. Rock tripes grow only on rocks like granite and schist that are rich in silicates. You won't find them on calciferous rocks like limestone or marble.
Trip down memory lane of lichen language: The lichen body is called a thallus and the three common growth forms are crustose (scale-like), foliose (leaf-like), and fruticose (erect and shrubby, or threadlike, with no upper or lower surface — like British Soldiers lichen).
Distinguishing characteristics: The smooth rock tripe is a foliose lichen. The upper surface of the thallus is relatively smooth. When wet, it is green and somewhat leathery and pliable. When dry, it is grayish-brown and brittle, and curls up around the edges exposing the lower, black, roughened surface. Smooth rock tripe is one of the largest lichens in the world; the pieces in the photo are about five inches across (larger than most lichens) but a specimen of 24 inches has been recorded in the Smoky Mountains in Tennessee. The thallus is attached to the rock by a short, stout, holdfast or umbilicus. All lichens that use this method of attachment are referred to as umbilicate. In the Conant Land, some of the smooth rock tripe is sharing its habitat with another umbilicate foliose lichen in the genus Lasallia — easily distinguishable by its warty surface.
Snail trail: The circle in the lichen photo marks the track where a snail (or slug) has been feeding on the algae embedded in the lichen. If you look at these marks closely, with a hand lens, you can see the individual scrapings, each one the width of the snail's tongue, as shown in the close-up photo. The needle in the photo is precisely 0.22mm in diameter (my dog is getting acupuncture treatments).
Lifeline: If you are lost in the woods in winter, without a cell phone and can't call a friend or ask the audience, a possible lifeline is rock tripe. Native American tribes have subsisted on it in times of famine. Some members of the Franklin Expedition of 1820-21 got through the winter by eating rock tripe. It is bitter and needs to be boiled repeatedly in several batches of water to make it somewhat palatable.
References: Lichens of North America by Brodo, Sharnoff and Sharnoff, published in 2001. Also help from Elizabeth Knieper, lichenologist, from her classes at Garden in the Woods.
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