An integrated molecular and morphological study of the subfamily Suaedoideae Ulbr. (Chenopodiaceae)

As part of an ongoing project on the phylogeny and taxonomy of Chenopodiaceae with emphasis on the evolution of photosynthetic pathways, we sequenced the nuclear ribosomal ITS region and two chloroplast DNA regions (atpB-rbcL and psbB-psbH) of 43 taxa belonging to subfamily Suaedoideae (Chenopodiaceae). Our sampling covered 41 of c. 82 known species and subspecies of Suaeda, beside several taxa not yet described, the monotypic genera Bienertia and Borszczowia as well as some representatives of Salicornioideae that served as outgroups. In addition, we carried out morphological and leaf anatomical studies on an extended sampling set, also including the monotypic genus Alexandra. Phylograms resulting from maximum parsimony analyses of separate and combined data sets share several common features. (1) Suaeda is monophyletic if Borszczowia is included. (2) The position of Bienertia is ambiguous, being sister to Suaeda in both chloroplast trees, but showing affinities to Salicornioideae in the ITS tree. (3) Suaeda deeply divides into two well-supported clades. One clade (Brezia clade) solely consists of the annual C-3 species of sect. Brezia. The second clade (Suaeda clade) includes all other sections. (4) The subclades of the Suaeda clade are in general agreement with currently accepted sections. A reassessment of morphological and anatomical characters on the background of the molecular trees resulted in the recognition of pistil morphology and leaf type as key characters. All major molecular clades are precisely defined by characteristic combinations of pistil and leaf types. The following taxonomic conclusions are drawn: the status of Bienertieae Ulbr. is confirmed; Suaeda is subdivided into the new subgenera Brezia (Moq.) Freitag & Schutze and Suaeda; Borszczowia is recombined into Suaeda and given sectional rank; within Suaeda, sects. Brezia, Schanginia, Borszczowia, Suaeda, Physophora, Schoberia and Salsina are recognized with some changes in circumscription; Alexandra is maintained at generic level because of the lack of molecular data and its striking morphological differences from Suaeda. A conspectus of Suaedoideae containing recognized species and all supraspecific taxa is given. The molecular results confirm that C-4 photosynthesis has evolved independently four times in the subfamily.