Exploring the Phylogenetic Position of a Bizarre and Poorly Understood Gypsum Endemic Plant

Science Center, Bent Corridor

Hedyotis is a genus within the coffee family (Rubiaceae) that includes a number of arid-adapted species in North America. Most North American Hedyotis species are small, herbaceous plants with narrow leaves that do not display a preference for one soil type. However, the northern Mexican species Hedyotis teretifolia is restricted to gypsum soils in northern Mexico and is characterized by several morphological characters that are bizarre for the family, including strong succulence, petals that persist on the flowers during fruit development, and an unusual ovary position. These traits suggest that this species may be a relatively ancient lineage that may be best treated as a new genus. To test this hypothesis, I generated DNA sequence data for H. teretifolia and several other North American taxa in the genus, including three chloroplast loci (trnL/F spacer atpB/rbcL spacer, and the rps16 intron) and one nuclear locus (ITS). Phylogenetic analyses based on these sequences suggest that H. teretifolia diverged early on in the evolutionary history of North American Hedyotis, but do not clearly resolve whether H. teretifolia should be treated as a new genus.