The revision of species-rich genera: a phylogenetic framework for the strategic revision of Pilea (Urticaceae) based on cpDNA, nrDNA, and morphology.

The revision of species-rich genera underpins research and supports the sustainable use and monitoring of biological diversity. One fifth to one quarter of the diversity of all seed plant species occurs in such genera, but difficulties with the revision of species-rich genera has resulted in many of them being ignored since the late 1800s. Pilea, with 600-715 species is in need of revision. The only realistic approach is in manageable subunits, which requires confirmation of monophyly and identification of monophyletic subdivisions. Parsimony analyses of trnL-F, ITS, and morphology data were used to test the monophyly of, and explore intrageneric relationships within, Pilea. Analysis of trnL-F data confirms and recovers two morphologically diagnosable monophyletic clades that include all of the taxa within Pilea. Overlaying geographic distribution on a most parsimonious tree indicates a strong association between geography and phylogenetic relatedness. It is suggested that a strategic revision within the framework of morphologically and geographically diagnosable units might enable the revision of the group using an iterative approach. Analysis of the outgroup taxa supports the inclusion of Poikilospermum within the Urticaceae and suggests that the Urticaceae tribes could be placed into two clades that are supported by floral morphology.