Thompsonella and the "Echeveria group" (Crassulaceae):: phylogenetic relationships based on molecular and morphological characters

Broad phylogenetic analyses of Crassulaceae have retrieved a large clade comprising as much as one-third of the species diversity present in the family as a whole. This so-called Acre clade (Sedoideae) includes familiar genera such as Echeveria, Graptopetalum, and Thompsonella, and while it is consistently recovered in studies at the family level, relationships within the clade as well as the monophyly of many of the constituant genera have yet to be established. Results of a phylogenetic Study of a genus within the Acre clade, Thompsonella, are here reported. Morphological evidence was gathered and molecular (nuclear ETS and ITS) DNA sequences were generated for forty-seven taxa from the Acre clade, including all recognized members of Thompsonella. Parsimony analysis of the combined data retrieved Thompsonello as a monophyletic group and retrieved species in Graptopetalum, Thompsonella, Echeveria, Pachyphytum and Sedum sect. pachysedum in a clade; this group was previously identified as the "Echeveria group". Results indicate that only a few genera in the Acre clade are monophyletic and that to establish their generic limits further sampling mainly in the large Echeveria and Sedum genera is needed. Results from morphological and molecular analyses disagree in the position of T mixtecana. However, an additional restricted analysis performed solely with cpDNA (rps16) placed this species within Thompsonella, suggesting a hybrid origin.