9701347 Rieseberg Graduate student Richard Noyes, under the direction of Prof. Loren Rieseberg at Indiana University, is studying the phylogenetic relationships of representatives of the c. 500 species of the sunflower subtribe Conyzinae, including Erigeron (fleabanes) and Conyza (horseweeds). Presumed to have originated in South America and spread northward, the Conyzinae appear instead to be a Nopth American group of sunflowers in origin, based on preliminary DNA sequence evidence from these researchers, which have spread southward and to other continents, in part as weeds that set seed without fertilization (a condition named agamospermy--dandelions being the better known example). Additional field collecting of samples, followed by molecular sequencing of a nuclear gene (ribosomal ITS regions) and a chloroplast gene (ndhF) and further study of traditional morphological characters, are tasks that will lead to phylogenetic reconstructions for the group. In turn, that genealogical framework facilitates the determination of geographical migrations and tracks in the evolution of these plants, and of the number of origins of the agamospermous condition. A well supported phylogeny of the fleabanes and their relatives, for the Americas and Africa, will improve classification of the group and provide reliable markers for identification. Also, studies can then progress on the ecological conditions favoring the origin of agamospermy, a peculiar asexual mode of seed production known in several lineages of the large sunflower family.
