Taxonomy and phylogeny of the Euphorbiaceae tribe Erismantheae G.L. Webster (Erismanthus, Moultonianthus, and Syndyophyllum)

The Erismantheae (monoecious, leaves opposite, stipules interpetiolar) contain three genera, Moultonianthus (monotypic), and Erismanthus and Syndyophyllum, each with 2 species. Moultonianthus is recognized by its persistent, large, cordate stipules; Erismanthus is characterized by the catkin-like staminate inflorescences with very long-pedicelled flowers; and characteristic for Syndyophyllum are the inflorescences with both staminate flowers (in bundles) and pistillate flowers (one per bundle of staminate flowers). Both varieties of Syndyophyllum occidentale are now considered to be distinctive species, because an additional difference was found (one axillary bud of each leaf pair present halfway along the petiole or not). The phylogenetic analysis of the Erismantheae, in comparison with two other tribes in the subfamily Acalyphoideae, the Chaetocarpeae and the Cheiloseae, shows that the Erismantheae are a very distinct, monophyletic group. Within the Erismantheae, Erismanthus and Syndyophyllum are closest related; all three genera are monophyletic.