By Frederick H. Utech
We've all seen Trillium many times-those showy, spring wildflowers that carpet the ground in backyards and forest floors. They grow in abundance along Trillium Trail in Fox Chapel and at Powdermill Nature Reserve. While we know Trillium when we see it, most people don't realize that there are 38 different varieties of this plant growing all over the northern hemisphere.
During the past 15 years, I have been part of an international team of botanists dedicated to observing, measuring and collecting Trillium samples from sites where they occur-through eastern North America, along the Pacific Northwest Coast and in eastern Asia, particularly Japan. Notably, the plant is not found in Europe.
There are three basic floral forms, or groups, of Trillium, each determined by how the flower is attached to its stalk. The "erect" group has a flower stalk above the three leaves; the "nodding" group has its flower stalk below the leaves, and the "sessile" group lacks a flowering stalk. All three types occur in western Pennsylvania. Their habitats throughout the northern hemisphere are varied, from wet cypress swamps in Florida's panhandle, to hot volcanic slopes with Ponderosa pine in Idaho, and maple-beech forests with bamboo in northern Japan.
Working on 38 species during one flowering season is difficult, because when Trillium flower in Pittsburgh, they are also flowering in Portland, Oregon; and in Sapporo, Japan. For that reason I am joined on the scientific team by five Japanese botanists from Kyoto and Hokkaido universities. Collectively, we study Trillium samples from all over the northern hemisphere. The program, funded in large part by the Japanese Ministry of Education's International Program, has resulted in nearly two dozen scientific papers and a 100-page monograph of the genus, complete with dozens of color photographs.
Our systematic studies focus primarily on evolutionary and ecological trends. First we gathered three sets of data for each of Trillium's 38 species in an effort to establish ancestral patterns and species relationships. This information on Trillium diversity represents three different levels of biological organization.
On the population level, we measured various ecological aspects of the species' life histories. Various population profiles result for each species from the different amounts of sexual (seed) and asexual (offshoot) reproduction. Furthermore, each species has a characteristic rate of seed production and percent germination. Depending on the species, five to 10 years are required for a Trillium seed to grow into a flowering plant. We also analyzed the various pollinators, such as small beetles and butterflies, and seed-dispersal agents-primariley ants of various, but related, types.
On the morphological level, we recorded data based on looking at the plant-its height, leaf shape, flower color, size and odor. Believe it or not, the flowers of the yellow Trillium luteum in Tennessee smell like lemon, while the dark purple Trillium foetidissimum in Louisiana smells like rotten meat.
On the molecular level, we sequenced a chloroplast gene (rBCL) with some 1,200 DNA base pairs for each species. Genes, such as rBCL, are linear arrangements of only four compounds (base pairs) whose precise order is repeated and recombined over and over again. A change to one base pair is a mutation. Closely related species have fewer mutational differences; distantly related species, many more.
Once this wealth of information was determined, we constructed and compared family trees showing species relationships for the three sets of data. There were comparable similarities in all three. The "sessile" flowered group, though presently in both eastern and western North America, had its origins in southeastern United States. All five Japanese species which belong to the "erect" group were probably derived from a single introduction whose ancestors were in North America. Surprisingly, the closest relative of the eastern Trillium undulatum ("Painted trillium") occurs in the rhododendron forest of northern India and Nepal.
This research is directed at understanding the natural history and biology of Trillium, a genus that dates back through the past 30 million years. There are numerous other forest floor herbs found with Trillium which are currently under study by our team to establish parallelisms, if any, in their evolution and the role of these groups in the origins of the temperate deciduous forests of the northern hemisphere.
So the next time you come across a hillside blanketed in Trillium, remember that it is but one of 38 species of the plant, and its closest relative could be on the next hillside, in the western United States, or in eastern Asia.
Frederick H. Utech is curator of Botany at Carnegie Museum of Natural History.