A morphometrics analysis of the widespread Triplaris americana (Polygonaceae)

Triplaris (Polygonaceae) is a genus of 18 species of fast-growing dioecious trees. Triplaris is widely distributed in the Neotropics, with a center of diversity in the western portion of the Amazon basin. The most recent revision of the genus was one of consolidation, lumping a large number of names into a small number of species concepts. One species in particular, T. americana, is presently an amalgamation of 15 historical taxonomic concepts. Moreover, as currently circumscribed, T. americana is morphologically variable and ranges over the whole of the Neotropics, despite the fact that most species in the genus have restricted geographic ranges. Given the recent taxonomic history of Triplaris, the infraspecific variation observed in T. americana, and the narrow endemism observed in most species of Triplaris, it is reasonable to question whether T. americana, as it is currently circumscribed, in fact constitutes a single species. This study examined the circumscription of T. americana using a morphological species concept, morphometrics, and hierarchical clustering. Hierarchical clustering revealed that the morphological variation present in 136 specimens of T. americana could be explained by dividing those specimens into two groups of plants. These groups however, could not be reliably distinguished morphologically. The distribution of values and morphologies among the various groups always overlapped. As a result, this work supports retaining T. americana as a single, widespread, and morphologically variable species.