Phylogenetic relationships between Sedum L. and related genera (Crassulaceae) based on ITS rDNA sequence comparisons

Sedum is the most species-rich and taxonomically complex member of the family Crassulaceae. The genus comprises ca. 420 species, which display notable diversity and homoplasy of growth forms, vegetative and reproductive features traditionally used to delineate crassulacean genera therefore it is impossible to characterize Sedum phenotypically. Artificial nature of Sedum was recognized long time ago and it was characterized as a catch-all taxon. The phylogenetic structure of Sedum and its relationship with allied genera are poorly understood. Two hundred twenty three sequences of nuclear ribosomal internal transcribed spacer (85 were obtained in this study) were used to address this question and provide a phylogeny-based framework for further taxonomic revisions. To identify positional homology between divergent sequences, secondary structure models were generated and used to guide the alignment. Our molecular phylogenetic data corroborated results of previous studies based on other markers and datasets and support the monophyly of the tribes Aeonieae, Semperviveae, and Sedeae. Our study is the first to resolve the Glade of the tribe Semperviveae based on sequence comparisons, and the clade of the tribe Sedeae with nrDNA. Sedeae accommodated majority of Sedum species either in the robust Acre Glade or paraphyletic Leucosedum cluster. Besides Sedum, these lineages comprised a number of genera that were mostly embedded among Sedum species. The highly polyphyletic nature of Sedum and its relatives corroborated in this study using a large taxon set, calls for re-evaluation of the genus concept in the family Crassulaceae and the tribe Sedeae in particular. (C) 2016 Elsevier GmbH. All rights reserved.