Preliminary Molecular Phylogenetic Studies in Pachyanthus (Miconieae, Melastomataceae)

Abstract

Pachyanthus (Melastomataceae: Miconieae) is traditionally circumscribed as a group of 20 species of Caribbean shrubs, mostly local Cuban endemics. However, the exact number of species is unknown because generic delimitations are still unclear for most genera of Miconieae. To test the monophyly of Pachyanthus, we produced a molecular phylogeny using nrITS and plastid trnS-G sequence data for 38 taxa of Miconieae in the genera Pachyanthus, Calycogonium, Tetrazygia, and Miconia. A species of Graffenrieda, a member of the sister group, Merianieae, was used as an outgroup. In the single-gene and combined analyses Pachyanthus is never recovered as a monophyletic group in any of its traditional circumscriptions. However, it is possible to distinguish a clade, Pachyanthus s.s., which is characterized by ovate to obovate petals that are conspicuously unguiculate; calyx lobes connate before anthesis, that separate into sepal-like segments; straight, ovate to oblong, yellow anthers without connective appendages or, if present, then inconspicuous, anthers dehiscing by small apical pores, and fruits with numerous seeds, 1–2 mm long, obpyramidal, with a smooth testa. The remaining species traditionally included in Pachyanthus do not have any of these features. They do not form a single monophyletic group, but instead are scattered across several clades, which also contain species of Calycogonium, Miconia, and Tetrazygia. Additional detailed molecular and morphological studies are needed in the Miconieae to ascertain whether these clades should be treated as new genera or recircumscribed as part of currently recognized genera in the Caribbean region, such as Calycogonium and Tetrazygia.