A multilocus phylogeny of the non-photosynthetic parasitic plant Cistanche (Orobanchaceae) refutes current taxonomy and identifies four major morphologically distinct clades

Abstract

Phylogenetic relationships of and within non-photosynthetic parasitic lineages are notoriously poorly known, which negatively affects our understanding of parasitic plants. This is also the case for Cistanche (Orobanchaceae), an Old World genus with about two dozen species, whose relationships have not yet been addressed using molecular phylogenetic approaches. Here we infer phylogenetic relationships within the genus, employing a taxonomically and geographically broad sampling covering all previously distinguished infrageneric groups and most of the currently recognized species. A combined matrix of three plastid markers (trnL-trnF, including the trnL intron and the intergenic spacer (IGS), trnS-trnfM IGS and psbA-trnH IGS) and one nuclear marker (ITS) was analyzed using maximum parsimony, maximum likelihood and Bayesian inference. Cistanche falls into four well-supported and geographically differentiated clades: East Asian Clade, Northwest African Clade, Southwest Asian Clade and Widespread Clade. Of those, only the East Asian Clade corresponds to a previously recognized taxonomic section, whereas the others either contain members of two or three sections (Widespread Clade and Southwest Asian Clade, respectively) or have not been taxonomically recognized so far (Northwest African Clade). Whereas the Southwest Asian Clade exhibits strong phylogenetic structure among and partly within species (the East Asian Clade and the Northwest African Clade are monospecific), phylogenetic resolution within the Widespread Clade is often low and hampered by discrepancies between nuclear and plastid markers. Both molecular and morphological data indicate that species diversity in Cistanche is currently underestimated.