Friday, February 5, 2010
Golden Moonglow Lichen
by Kay Fairweather
One hundred and ninety years ago today, on February 5 1820, Timothy Wilkins died. Mary, his wife of 65 years, died 8 days earlier. Two gravestones erected in their memory stand side-by-side in the Central Burying Ground opposite Ferns. These gravestones, like most that are not highly polished, have become the home for a variety of lichens. In 2002 when I began studying lichens I chose a certain Golden Moonglow Lichen on Timothy Wilkins’ gravestone to learn something about the rate of growth of lichens. Once or twice a year I take photos of it to measure its progress.
Which Timothy?: In the 18th century Carlisle was home to a father, son and grandson all named Timothy Wilkins. Timothy, the father, was the one who gave land at the center of town on two occasions; once for a cemetery and again in 1758 for the building of a meeting house. He also built and lived in the house at 52 East Street. He is presumed to be buried in the Central Burying Ground but his grave is not marked. “Moonglow Timothy,”“Lichen Timothy,” or as I mostly call him “My Timothy,” was the first born child of “Land grant” Timothy. My Timothy and his son, Timothy III, both have gravestones in the Central Burying Ground.
Moonglow Lichen: The Golden Moonglow Lichen is Dimelaena oreina (pronounced dime-a-line-a oh-rine-a). All six North American members of the genus are known as moonglow lichens. The golden one is the most widespread and is very common in the Central Burying Ground and in the Green Cemetery.
Identification: The thallus (the body of the lichen) is more or less circular with the newest growth on the outer edge being a yellowish-green color and much paler than the older parts near the center. It often forms concentric patterns as new growth replaces die-back at the center. The spore-producing bodies, called apothecia, are the equivalent of the mushrooms produced by non-lichenizing fungi. These ones are black and are embedded in the lichen thallus.
Lichen growth: Most lichens grow very slowly. This is partly because they are dual organisms made up of a tightly-coupled relationship between a fungus and an alga. The codependency is vital. The two components need to keep in step with each other. If the fungus growth outpaces the alga, or vice versa, the whole relationship breaks down – so they spend their lives waiting for one another. (Remind you of anyone?) Crustose lichens, such as the Golden Moonglow Lichen, are closely bonded to the surface on which they grow and of all lichen types this is the kind that grows the slowest. The increase in the radius of a circular patch of a crustose lichen is usually in the range of half to two millimeters per year. The particular patch of Golden Moonglow Lichen I have been measuring on “My Timothy’s” gravestone has grown 9 mm in diameter in eight years, an average radial growth of 0.56 mm per year. It now has faster growing lichens on top of it. These are more loosely attached and may come off, or they may eclipse the Moonglow and starve it. The race is on.
Longevity: A characteristic the Wilkins family has in common with crustose lichens is a long life-span. The first Wilkins generation in the U.S., Bray Wilkins who came to Salem in 1628, lived to be an “ancient man” of 92 years. My Timothy’s dad was 82 years old when he met an untimely death “being melted at a brush fire.” My Timothy lived to be 88 years old and his brother Isaac was 93. In a time when healthcare was constrained by knowledge and science rather than by maximizing profits, the Wilkins family seems to have had remarkable longevity.
Lichens though are in a different league. Some rock-dwelling crustose lichens are estimated to be over 4,000 years old. This longevity has given rise to lichenometry, a technique for estimating the age of rock surfaces (really just the minimum age) by applying a lichen’s known average growth rate to the size of the lichens on that surface. For example, lichens “say” that the Easter Island monuments are at least 450 years old. Lichenometry has been used on glacial moraines in Canada and Alaska to understand the rate of retreat of glaciers, and on rock slides in the Sierra Nevada to estimate the approximate date of major earthquakes.
Messages from the graveyard: When I visit the Central Burying Ground I check out the other gravestones not only for lichens but for epitaphs. It seems there was a time when people felt the need to remind others of their mortality – whether young or old. For example: Mary Litchfield at 3 ½ years: “Little children come here and learn / that death may cut you down while young.” And Esther Taylor at 75 years: “Friends nor physician could not save / My mortal body from the grave.” Some seem to say to those still above ground, don’t get complacent for you too will be brought down. All that’s missing is a final comment of “so there.” For example: Nathaniel Parker at 56 years: “Death is a debt to nature due / Which I’ve paid & so must you” and Mary Wilkins, sister-in-law of My Timothy at 59 years: “As you are now so once was I. / As I am now, so you must be. / Prepare for death & follow me.” My Timothy’s epitaph reads “Though greedy worms devour my skin / And gnaw my wasted flesh / When God shall build my bones again / He’ll doth them all afresh.” I appreciate his acknowledgement of creatures of the soil.
Sources: Lichens of North America, by Brodo, Sharnoff and Sharnoff; Carlisle Composite Community, by Donald A. Lapham; Carlisle, Its History and Heritage, by Ruth Chamberlin Wilkins; Vital Records of Carlisle, Mass. to the end of the year 1849. ∆
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