A molecular phylogenetic study of Graptopetalum (Crassulaceae) based on ETS, ITS, RPL16, and TRNL-F nucleotide sequences.

Nuclear ETS and ITS, as well as plastid rpl16 and trnL-F DNA sequences were used to determine relationships among species of Graptopetalum (Crassulaceae) and closely related genera. Graptopetalum is member of a group of taxa restricted to North America, one of the centers of diversity of Crassulaceae; however, their phylogenetic relationships are not yet understood. Nineteen species of Graptopetalum and 24 species from nine other genera of Crassulaceae were sampled for use in three separate parsimony analyses: ITS alone, ETS alone, and a combined nuclear + plastid DNA analysis using all four gene regions. The ETS data set had the highest number of parsimony-informative sites, about 30% more than in ITS, but the most fully resolved tree resulted when the four DNA regions were combined. Only four subclades of the tree received moderate to strong bootstrap support, one of which includes all species of Graptopetalum having a single whorl of stamens. However, Graptopetalum is not monophyletic. Instead, Tacitus bellus and select species of Cremnophila, Sedum, and Echeveria are interspersed among species of Graptopetalum and show evidence of grouping according to geographical range of distribution more so than habit or floral morphology.