Phylogenetic relationships in Seslerieae (Poaceae) including resurrection of Psilathera and Sesleriella, two monotypic genera endemic to the Alps

Abstract

AbstractSesleria (Poaceae) is a species‐rich, taxonomically difficult genus due to high morpho‐anatomical variability and weak differentiation of many species. It is distributed throughout western Eurasia and North Africa with highest taxonomic diversity on the Balkan Peninsula. Of the more than 40 species only two are diploid, all others are tetra‐ to dodecaploid, and many species comprise several ploidy cytotypes. We sequenced the plastid trnL‐ndhF region and produced amplified fragment length polymorphisms (AFLPs) from a comprehensive, ploidy‐cytotyped sampling including 292 populations, and produced nuclear ribosomal internal transcribed spacer (ITS) sequences for a subsample. Our first aim was to determine the relationships among Sesleria and putatively closely related genera. Further, we explored whether diploid S. sphaerocephala and S. ovata should be treated as separate genera Sesleriella and Psilathera as proposed previously, or rather included in Sesleria, following most recent Floras. Finally, we tested previous hypotheses of infrageneric classifications. In the ITS phylogeny tetra‐ to dodecaploid Sesleria s.str. grouped with diploid S. ovata whereas diploid S. sphaerocephala was more distantly related. In contrast, in the plastid phylogeny Sesleria s.str. grouped with S. sphaerocephala, whereas S. ovata was sister to Echinaria. This suggests an allopolyploid origin of Sesleria s.str. with S. sphaerocephala acting as maternal and S. ovata as paternal species. The lack of monophyly of Sesleria s.l. thus supports the recognition of S. ovata and S. sphaerocephala as separate genera Psilathera and Sesleriella. Their segregation, which is also supported by morphology, increases the number of angiosperm genera endemic to the European Alps from three to five. In congruence with the plastid sequences, AFLPs resolved the traditionally recognized sections (sect. Argenteae, sect. Sesleria) as non‐overlapping clusters and identified S. vaginalis as a probably recently evolved intersectional hybrid. Within the two sections, several informal species groups could be recognized, which show limited congruence with those proposed in the most comprehensive taxonomic treatment of the genus. From an evolutionary point of view it is obvious that ancient as well as recent hybridization coupled with polyploidisation have played a crucial role in diversification within Sesleria.