Molecular Phylogeny and Taxonomic Revision of the Genus Diastatea (Campanulaceae: Lobelioideae)

Diastatea (Campanulaceae-Lobelioideae) is a genus of small, herbaceous annuals found mostly in Mexico. Differences in the number of recognized species in the historical treatments, and the lack of a phylogeny, suggested that a revision of the genus was necessary. Species boundaries and species level relationships were tested based on a sampling of nearly 50 individuals. Sequences of the chloroplast spacer regions, atpB-rbcL and ndhF-rpl32, as well as the ITS, were generated and then analyzed using maximum likelihood and Bayesian inference methods. The analyses of the separate datasets produced congruent topologies. Two strongly supported clades of Diastatea are newly recognized as subgenera in the taxonomic treatment. Diastatea Scheidw. subg. Diastatea and Diastatea subg. Angustifolia E.P.Johnson & T.J.Ayers can be distinguished morphologically by leaf shape and pubescence, hypanthium shape, and the presence or absence of a gibbous projection on the ventral side of the corolla. A morphological treatment of the genus corroborated by the molecular analysis revealed one new species, Diastatea aptera E.P.Johnson & T.J.Ayers, one new subspecies, Diastatea tenera subsp. durangensis E.P.Johnson & T.J.Ayers, and elevated an existing subspecies, Diastatea ciliata (McVaugh) E.P.Johnson & T.J.Ayers, to specific rank.