Molecular phylogeny and morphology of Elatostema s.l. (Urticaceae): Implications for inter- and infrageneric classifications

Elatostema s.s. (Urticaceae) comprises approximately 500 species of herbs and subshrubs distributed in tropical and subtropical Asia, Australasia, and Africa. The delimitation of Elatostema s.s. and the closely related genera Elatostematoides, Pellionia, and Procris has long been problematic because of the large number of taxa and presumed homoplasy among diagnostic morphological characters. In the present study, we refer to these four genera together as Elatostema s.l. To evaluate the circumscription of Elatostema s.l. and its generic and subgeneric classification, we conducted phylogenetic analyses of DNA sequence data from the internal transcribed spacer of the nuclear genome (nrITS) and two markers from the plastid genome (psbA-trnH and psbM-trnD) for 126 taxa, representing 88 species of Elatostema s.s., four of Elatostematoides, nine of Pellionia, and five of Procris. Ten selected morphological characters were investigated using ancestral state reconstructions. Our results show that Elatostema s.l. can be divided into three well-supported and morphologically distinct genera: Procris, Elatostematoides, and Elatostema sensu auct. The results of our molecular phylogeny suggest four strongly supported clades within this newly defined Elatostema s.a.: core Elatostema, Pellionia, Weddellia, and an as yet undescribed clade African Elatostema. Homoplasy among the morphological characters used in this study makes it impossible to circumscribe genera using synapomorphies, but combined suites of characters do enable the morphological diagnosis of Elatostema s.a., Elatostematoides, and Procris.