Molecular phylogenetics of the Caribbean genera Rhodogeron and Sachsia (Asteraceae)

Rhodogeron Griseb. and Sachsia Griseb. (Asteraceae) are two Caribbean genera. Rhodogeron is restricted to Cuba, whereas Sachsia is found in Cuba, the Bahamas, south Florida, and Hispaniola. A phylogenetic study of nucleotide sequences of the chloroplast gene ndhF and of the internal transcribed spacers (ITS) of the nuclear ribosomal DNA shows that these two genera form a monophyletic group. The ndhF phylogeny places Rhodogeron and Sachsia within the tribe Plucheeae but with only very weak bootstrap support (59%). The ITS phylogeny indicates the serpentine areas of Cuba are the ancestral habitat for these genera, with a colonization route from Cuba toward the Bahamas and Florida. In addition, this study supports previous taxonomic treatments that considered Sachsia divaricata Griseb. and Sachsia polycephala Griseb. to be conspecific. Finally, Rhodogeron is the sister taxon to Sachsia, and we propose that it should be maintained as a distinct monospecific genus.