Usefulness of morphological characters for infrageneric classification of Elatostema (Urticaceae)

In 1896, Hans Hallier was the first author to reduce the two genera Pellionia and Procris to subgeneric status within the genus Elatostema (Urticaceae). In 1935 and 1936, Hilde Schröter and Hubert Winkler proposed the following four subgenera: subg. Elatostema, subg. Elatostematoides, subg. Pellionia and subg. Weddellia, while maintaining Procris as a distinct genus. More recently, Wang (1980a) rejected Schröter and Winkler's subgeneric classification of Elatostema and proposed a sectional and serial infrageneric classification of recognising as sections Androsyce, Elatostema, Laevisperma, Pellionioides and Weddellia (as 'Weddelia'). He maintained both Pellionia and Procris as distinct genera. All previous researchers of Elatostema and related taxa primarily based their classifications on the morphology of leaves, stipules, inflorescence and receptacle. Our analysis, based on similar morphological characters, does not support the previous infrageneric classifications. Procris forms a monophyletic clade, nested within a clade consisting of several species of Elatostema subg. Pellionia and one of subg. Elatostematoides. Elatostema auriculatifolium (subgeneric classification unclear) is also included within this clade. This clade is sister to the E. latifolium–E. tsoongii pair of species (also subg. Pellionia), subg. Elatostema (the remaining species of this subgenus), species of subg. Weddellia and E. rostratum (subg. Elatostematoides). Elatostema subg. Weddellia is paraphyletic within subg. Elatostema. The recognition of Elatostematoides, Pellionia and Procris as distinct genera is not supported.