Harvard University student and Alabama native Ian Shields takes a measurement of lichens on a headstone in the Town Center Cemetery. (Photos by Lisa Aciukewicz)

John Aloian gets a close-up view of a lichen on the face of a gravestone.

Research assistant Michaela Schmull points out a fungus.

A recent drizzly afternoon found groups of students, hand lenses and tape measures in hand, intently examining the headstones in the Town Center Cemetery, seemingly more interested in what grew on the stones than what lay beneath them.

For the past five years, Anne Pringle, an associate professor in Harvard University's Department of Organismic and Evolutionary Biology, has been bringing her students to the cemetery in search of lichens, a familiar sight on old stone walls and exposed rock formations. Lichens are dual organisms made up of fungi in symbiotic partnership with a food source, most often algae. Unable to make their own food, the fungi in lichens depend on photosynthetic algae to provide carbon sugar that the algae create from carbon in the atmosphere.

Lichens are abundant in the cemetery. A first-year graduate student in Pringle's lab, Primrose Boynton, peered closely with her hand lens at a square inch of green on the top of a Whitney headstone. "I can see six different kinds here," she remarked.

Pringle explained why she came so far afield to examine grave markers. "Lichens are very sensitive to air pollution. We can't find these in Cambridge. And," she paused, "you don't clean your stones." Pringle elaborated that caretakers of many U.S. cemeteries work to keep lichens off the stones, unaware of the great biodiversity old churchyards and cemeteries can harbor. Other countries, most notably the UK, are trying to preserve their quiet graveyard refuges for the habitats they provide.

With her infectious enthusiasm, Pringle pointed out two of her favorite grave markers. Deep-cut letters on a Bull family stone were filled with moonglow lichens, while the rest of the stone was bare, suggesting that a midnight trip on a moonlit night might reveal the Bull family names. On another stone, small, perfect circles of lichens dotted the left and right sides of a tombstone face. Carving on the top of the stone diverted rain to either side of the face, dispersing the lichens that formed like tears down the stone.

Nearby, tiny shoots of red stood out from a gray-green base. "British soldier lichen," Pringle said.

Undisturbed graveyards are a perfect laboratory to study lichens. Even a casual walk through the cemetery quickly suggests that Harvard's lichens prefer slate, will colonize granite cuts, but have little taste for marble. Closer examination reveals a great diversity of lichen species and that there are fewer lichens on the stones near Mass Ave. Were these stones cleaned or might car traffic be a factor?

Lichens are sometimes used to date buildings and other objects because they are extremely long-lived. According to an article in the Harvard Gazette, they are so long-lived that Pringle may be thinking of exploring whether or not they are immortal. Everlasting life in the cemetery?