Darwiniothamnus (Asteraceae: Astereae) is one of the seven plant genera endemic to the Galapagos Islands. Based on morphological grounds the genus, although distinct, has been suggested to be closely related to South American Erigeron; however this hypothesis needs to be tested by rigorous phylogenetic methods. In this study a preliminary phylogeny of the ITS region of the nuclear ribosomal DNA is presented. This phylogeny suggests that Darwiniothamnus is nested within the Erigeron clade, which is composed of Aphanostephus, Conyza and Erigeron. Upon further analysis it appears that Darwiniothamnus may be sister to E. thrincioides and E. bellioides which are both from the Antilles. Further studies are currently in progress to confirm this possible biogeographical connection between the Caribbean basin and the Galapagos Islands. These additional studies will include putative relatives from Mexico, Chile and the Revillagigedo Islands of the Pacific Ocean.

Key words: Darwiniothamnus, Galapagos Islands