Molecular Phylogeny and Pollen Evolution of Euphorbiaceae Tribe Plukenetieae

Tribe Plukenetieae (Euphorbiaceae, Acalyphoideae) is a pantropical lineage of mostly stinging, twining vines and lianas with diverse floral and pollen morphology. To elucidate generic relationships in the tribe and examine patterns of pollen morphology evolution, we conducted phylogenetic analyses of nuclear ribosomal ITS and plastid psbA-trnH DNA sequence and indel gap-scored data. We sampled all genera in subtribes Dalechampiinae and Tragiinae, and most in Plukenetiinae; species sampling was broad in the latter two subtribes. Our efforts produced a 2,207 character dataset of 154 terminals (representing ca. 93 species). Analyses of these data support the monophyly of each subtribe and weakly suggest Dalechampiinae (Dalechampia) is sister to Plukenetiinae + Tragiinae. Within Plukenetiinae, Haematostemon is resolved as sister to Romanoa + Plukenetia, and Plukenetia is divided into five subclades that mostly correspond to the current infrageneric classification. Tragiinae is resolved into an Old World lineage and a mostly New World lineage, and is divided into ten subclades also supported by floral and/or pollen morphology. Species-rich Tragia is recovered as para- or polyphyletic and intermixed with all other currently recognized Tragiinae genera. The recently segregated genera, Bia, Ctenomeria, and Zuckertia, are upheld, and Gitara is resurrected from Acidoton, resulting in two new combinations: Gitara nicaraguensis and Zuckertia manuelii. Pollen aperture and exine morphology are largely correlated with phylogeny. The loss of pollen endopores is a potential synapomorphy of Plukenetiinae + Tragiinae, and we hypothesize that weakly defined apertures and inaperturate pollen originated independently four and three times, respectively.