The Carlisle Mosquito Online

Friday, December 11, 2009


Old Man's Beard

Any time we have a northeaster or any kind of heavy winds, branches and twigs which have broken from the canopy will be scattered on the ground. Many of those branches will have

This lichen, Old Man’s Beard, was most likely blown down from a tree before it was found in the middle of a Conant Land trail. (Photo by Kay Fairweather)

lichens and some will have Old Man’s Beard. On Cape Cod and in Maine on Mount Desert Island, you barely have to open your eyes to find lichens in this genus (Usnea) but they are much less prolific in Carlisle. I found this sample on a twig in the middle of a trail on the Conant Land about two weeks ago, just after a day of strong wind.

Name: Old Man’s Beard or simply Beard Lichen is the common name used for all lichens in the genus Usnea. There are 86 different Usnea species known in North America. This one is Usnea subfloridana, which is also known as the Common Beard Lichen. The name Usnea is derived from the Arabic “ushna,” which means moss. Even though lichens are composed of two different life forms (a fungus and a photosynthesizing partner which is usually an alga and sometimes a cyanobacterium), they always take their name from the fungal partner. This is because there are over 17,000 fungi capable of forming lichens but a relatively small number (a few hundred) of algae or cyanobacteria. If there was only one fungus per lichen, the naming methodology would work well and up until now it has. DNA analysis of lichens is about to upset this applecart. Science News, November 7, 2009, has a report of tests conducted by François Lutzoni at Duke University in Durham, N.C., where they have yet to find a lichen with the DNA of only a single fungus. “Every species tested so far, contains multitudes.”

Identifying characteristics: Old Man’s Beard is a yellowish green lichen where the thallus (i.e. the body of the lichen) is a cluster of branches or threads which are usually round in cross-section and which have a central cord or axis. It is fairly easy to differentiate members of the Usnea genus from other threadlike lichens mainly because of the central cord. Within the genus, some species have a long, droopy thallus and some, like this one, are shrubby. The longest droopiest one, called Methuselah’s Beard, may be a yard or more long. In the Common Beard Lichen, the holdfast which anchors the thallus to the branch is black. Close examination of vegetative reproductive structures with a hand lens, and chemical spot tests are needed to confirm the identification.

Pollution monitoring: Some lichens are extremely sensitive to air pollution and especially to sulphur dioxide. Among these are the droopy or pendent forms of Usnea. Methuselah’s Beard (Usnea longissima) which used to be common in Europe is now almost extinct there. It also used to be common in Massachusetts but seems to be gone from here too. It can still be found in Maine and is known at a single site in New Hampshire. Because of their sensitivity, lichens are now used in a variety of air pollution monitoring programs.

Other uses: Lichens have a long history of use as a source of dye. Usnea subfloridana is reputed to yield a grayish-olive color. As such, it is not among the desirable lichens for dyeing. Usnea species are better known as a source of usnic acid which has antibiotic properties and is still used for that purpose.

Bird nests: About 45 species of birds, including Ruby-throated Hummingbirds use lichens on their nests, probably to help camouflage them. One bird, the Northern Parula, makes its nest almost entirely from Usnea. Maybe that is what gave Edward Lear the idea for his limerick about an old man’s beard. “There was an Old Man with a beard / Who said, “It is just as I feared! / Two owls and a hen, / Four larks and a wren, / Have all built their nests in my beard!”

References: Lichens of North America, by Brodo, Sharnoff and Sharnoff; Macrolichens of New England, by James W. Hinds and Patricia L. Hinds; Science News, November 7, 2009; A Partnership Apart, by Susan Milius. ∆

© 2009 The Carlisle Mosquito