On November 1, the Farlow Herbarium of Cryptogamic Botany celebrated its centennial with a symposium that featured speakers eminent in the field. Cryptogamic botany, for the uninitiated, is the study of spore-producing plants—organisms that turn out to have an outsize impact on the human world: the world’s coffee crops, for example, are threatened by a baffling fungal infection (see below). The Farlow collection, one of the world’s leading centers for the study of such organisms, is an example of the hidden scholarly riches of Harvard’s deep collections and their surprising applications.
This specialized herbarium encompasses fungi, including lichens, algae, bryophytes (the liverworts, hornworts, and mosses), myxomycetes (slime molds), and even bacteria—but excludes ferns and allied spore-producing plants. The cryptogams, so named because their means of sexual reproduction is sometimes mysterious, were in evolutionary history the organisms that enabled aquatic plants to make the transition to land, as professor of organismic and evolutionary biology Jeannine Cavender-Bares, recently appointed director of the Harvard University Herbaria (of which the Farlow is a part), explained in her introductory remarks.
But much about the cryptogams remains unknown. Among the fungi alone, there are thought to be more than two and half million species, more than 90 percent of them undescribed. And just 0.4 percent of the known fungi have been assessed for their conservation status, said Cavender-Bares, as compared to about 80 percent of animals.
And even fungi that are the object of intense scientific scrutiny remain poorly understood. M. Catherine Aime, professor of mycology at Purdue University, and director of its Arthur Fungarium and Kriendler Herbarium, described her laboratory’s research into coffee leaf rust (Hemileia vastatrix), a disease of coffee plants first discovered in Sri Lanka that has now spread worldwide. The stakes for curing the disease are high: coffee is the world’s second-most traded commodity, Aime said, after oil. Using herbaria collections as their laboratory, she and her students are seeking ways to control this devastating crop pathogen, which curbs coffee production from 30 to 50 percent.
Coffee is not the only plant affected by rust. This group of fungi causes some of the most important plant diseases, Aime explained. (Purdue holds the largest collection of rust, including a specimen gathered in Tierra del Fuego on Captain James Cook’s first expedition, begun in 1768). Rust fungi have large genomes, complex lifecycles, and can’t be cultured—which can make them challenging to study.
Coffee leaf rust is an especially cryptic fungus: it can reproduce clonally on coffee plants, but also sexually on an alternate host plant—whose identity remains unknown. Genotyping of the fungus enabled researchers to trace its spread around the world, probably as spores which adhered to the clothing of migrant workers. But how to control it? A student in Aime’s lab has been exploring the possibility of using biocontrols—parasites that feed on rust fungi—to curb the disease. And herbaria have played a crucial role: about 10 percent of the samples her graduate student examined had hyperparasites (parasites of parasites)—“accidentally co-collected along with the rust leaf specimens.” She showed one that came from Farlow’s collection dating to 1912. “He had no idea” at the time, she said, “that he was collecting a new hyperparasite.”
Like Harvard itself, the Farlow was founded by a gift of books. William Farlow A.B. 1866, left a library of 10,000 volumes at his death in 1919, recounted Asa Gray research professor of systematic botany Donald Pfister, curator emeritus of the Farlow library and herbarium, in his presentation on the institution’s history. (Born in Boston in 1844, Farlow became an assistant to botanist Asa Gray after earning his Harvard M.D. He then spent two years studying with European botanists before returning to Harvard. He was appointed professor of cryptogamic botany in 1879 and is considered the senior figure in the field in the United States.) The books (now 70,000 in number) were to be combined with the Cryptogamic Herbarium’s then 50,000 biological specimens (today more than 1.5 million). Farlow himself became involved in the practical applications of his scholarly pursuit, actively hunting the fungus that reduced the once grand American chestnut tree to a shrub. And in World War II, said Pfister, who has served as the Farlow’s tenth director since 1972, the Quartermaster Corps spurred study of how fungi decay materials ranging from canvas to shoe leather in tropical climates, generating a vast trove of fungi from around the world. The collection even includes a specimen isolated from a plastic canteen in New Guinea.
“The Farlow is hallowed ground for fungal biologists” Clark University professor of biology David Hibbett said in a lively talk, “Hunting the Tiger Sawgill,” in which he described how this semi-aquatic mushroom takes on two completely distinct physical forms and may hold clues to morphological evolution in fungi. Brent Mishler, Ph.D. ’84, Distinguished Professor emeritus at the University of California Berkeley, who spent six years studying at the Farlow, spoke about phylogenetic diversity, explaining that knowing numbers of species alone doesn’t enable accurate measures of biodiversity. Fourteen closely related species (as assessed genetically) living in a defined geographic area, to take a simple example, don’t represent as much phylogenetic biodiversity as 14 distantly related species. And renowned plant collector Terry Henkel, a professor of botany at California State Polytechnic Institute, Humboldt, who hunts plants mainly in Central and South America, spoke about some of his collecting expeditions, later emphasizing the critical need for “finding species that are out there before they disappear. The fundamental purpose of collections, is to have reference specimens…because of the key role they play documenting the existence of species for taxonomists.”
Last to speak was Rebecca Yahr, the lichen biodiversity specialist at the Royal Botanic Garden Edinburgh. Lichens are like canaries in coal mines: because of their sensitivity to both environmental pollution and temperature changes they serve as responsive bioindicators. They are also unable to easily shift their natural range from one reproductive cycle to the next: carried by the wind, their spores can establish new lichens at distances up to 50 meters, Yahr reported, but don’t easily colonize spots as little as 100 meters away. That implies that there is a rapid decline of lichen biodiversity already in train, with more to come.
Two of her colleagues have come up with an innovative way to measure the decline. As she explained, comprehensive records of lichens in the United Kingdom begin around 1970, when sulfur dioxide pollution (which causes acid rain) was already at its peak. How then, could lichenologists establish a baseline for lichen biodiversity before human influences began to reduce their prevalence on the landscape?
The answer, it turned out, lay in the roughly constructed outbuildings that dot the English countryside. The local timbers used for these buildings, although often crooked, were frequently left unfinished, with the bark still on. And between them, saplings that grew nearby were woven, then covered in wattle and daub. Remarkably, the bark of some of these trees and saplings contains a record of lichen diversity stretching back as far as the fifteenth century. And what they reveal is a dramatic shift in the distribution of lichen populations: a species that lived in the London area in 1450, for example, is now found only in northern coastal England and in Scotland.
If there was a lesson in the day’s celebration, it was that herbaria like the Farlow have tremendous utility that only increases with the passage of time, especially in the present era of rapid environmental change. As Mishler put it later that day, “These are not libraries. They are not storage. They are laboratories.”
