Phylogeny of the species-rich Pilea Lindl. (Urticaceae) supports its revised delimitation and infrageneric classification, including the resurrection of Achudemia Blume

Abstract

ABSTRACTPilea Lindl., with 933 published names is the largest genus within the Urticaceae. Pilea was last monographed in 1869 and whilst the monophyly of the genus has been proposed by previous authors, this has been based on incomplete taxon sampling and the failure to resolve the position of key taxa. We aimed to generate a robust phylogeny for Pilea and allied genera that could provide a framework for testing the monophyly of Pilea, revising its delimitation and for answering broader scientific questions about this species-rich genus. To do so, we sought to sample taxa representative of previous infrageneric classifications and with anomalous inflorescences or flower configurations and to use the resulting phylogeny to evaluate the delimitation of Pilea and to establish an infrageneric classification. In addition, we included a representative of the Polynesian genus Haroldiella which, morphologically, is very similar to Pilea. Using Sanger sequence data from two plastid and one nuclear regions we constructed a phylogeny using Bayesian Inference, Maximum Likelihood and Maximum Parsiomony approaches. We used our phylogeny to evaluate the informativness of 19 morphological traits and applied both to delimit a monophyletic genus and infrageneric sections. Our results recovered Pilea as paraphyletic with respect to Lecanthus, a consequence of the recovery of a monophyletic clade comprising sections Achudemia and Smithiella, neither of which had been adequately sampled in previous studies. We also recovered Pilea as polyphyletic with respect to Haroldiella. We identified isomery between male and female flowers, flower part number and male sepal arrangement as being phylogenetically informative traits that can be used to delimit two genera, Achudemia, including section Smithiella, recovered as sister to Lecanthus, and Pilea, including Haroldiella, recovered as sister to both. On the basis of our evaluation of both morphological traits and phylogenetic relationships we propose a new infrageneric classification for the genus comprising seven sections, five of which we describe for the first time, § Trimeris Y.G.Wei & A.K.Monro, § Lecanthoides C.J.Chen, § Angulata L.F.Fu & Y.G.Wei, § Tetrameris C.J.Chen, § Verrucosa L.F.Fu & Y.G.Wei, § Plataniflora L.F.Fu & Y.G.Wei and § Leiocarpa L.F.Fu & Y.G.Wei. We also identify a trend of decreasing merism and fruit size, and increasing species-richness as Pilea diverges. In addition, we recover strong geographical structure within our phylogeny, sufficient to propose that Pilea originated in the IndoMalaya biogeographic domain.