Molecular phylogeny of Trigonostemon and its relatives (Euphorbiaceae)

Trigonostemon , Dimorphocalyx , Tritaxis and Ostodes are tropical Asian genera that are very similar in morphology. The former three genera have been treated either as a single genus Trigonostemon s.l. or as separate genera. A molecular phylogeny based on the nuclear ITS and chloroplast trnK intron, trnT ‐ L and trnL ‐ F sequences reveals that Trigonostemon is a monophyletic group, and Dimorphocalyx and Tritaxis together form another monophyletic group separate from Trigonostemon . Within the genus Trigonostemon , a strong correlation between the molecular phylogeny and pollen morphology was found. It demonstrates two potential evolutionary directions for the common “croton pattern” ornamentation of pollen in the genus: the subunits that form the “croton pattern” ornamentation tend to reduce to spines or they tend to merge in the later‐developed groups. The correlation between the molecular phylogeny and macromorphology of Trigonostemon is discussed, and a new infrageneric classification with four sections is provided. Dimorphocalyx is reduced to Tritaxis , the older generic name.