Tropical tree-ferns are the only trees alive today that have retained the primitive type of reproduction (by spores rather than by seeds) characteristic of the earliest land plants. Tree ferns of the Cyathea complex of species differ from other ferns in their lack of polyploidy (multiple sets of chromosomes) and by the production of fertile, diploid hybrids. Drs. Diana Stein and David Conant will construct a phylogeny or scheme of evolutionary relationship for the tree-ferns to serve as a framework for analyzing speciation mechanisms in this group and to resolve conflicting taxonomies of the species and genera named thus far. Attempts by other scientists to construct phylogenies for the group have used morphological features (such as leaf scale characters) subject to convergent or parallel evolution. Drs. Stein and Conant will examine variation in mutational differences in the chloroplast DNA of tree-ferns, to determine the pattern and direction of change among taxa. Chloroplast mutational differences provide a more direct reflection of genetic divergence among species, and hold great promise for tracking the course of evolutionary change in these plants.
