Phylogenetic relationships in the genus Sedum L. (Crassulaceae) and closely related genera based on ITS rDNA sequence comparisons

Vyacheslav NIKULIN1 & Svetlana GONTCHAROVA2
1 Institute of Biology and Soil Science FEB RAS, Vladivostok, Russia
2 Botanical Garden-Institute FEB RAS, Vladivostok, Russia

Results of phylogeny reconstruction in the subfamily Sedoideae (Crassulaceae) based on 199 ITS rDNA sequences are presented. Prior to alignment secondary structure model based on the thermodynamic folding was created for each sequence. Models of secondary structure for Crassulacean taxa are generally consistent with those in other groups of eukaryotes: ITS1 - almost half of the nucleotides refers to the single-stranded sites; 4 short stems were revealed with an area of conservation laid prior the stem 1, in entire stem 3 (motif GGCRY-[4-7N] -GYGYCAAGGAA, homologous in all groups of plants) and flanking it regions. In ITS2 four stems were identified: the 1st had conservative basal part only, 2nd stem was highly conserved and contained a pyrimidine-pyrimidine mismatch, and the 3rd is the longest stem contained a conserved motif of about 20 nt near its distal part, 4th stem was the most variable. Secondary structure data of the ITS transcripts guided alignment of generally very divergent in this group ITS sequences. In the phylogenetic analyses complex evolutionary models and methods of maximum likelihood, neighbor-joining and maximum parsimony were used. In the resulting tree species were grouped into four clades/clusters: «Acre», «Leucosedum», «Sempervivum» and «Aeonium» with members of the genus Sedum s. l. to be found in all of these groups. This result clearly indicates artificial nature of this genus. Our analyses revealed a dichotomy between American and Eurasian species of Sedum in the most species-rich "Acre" clade. It is notable that sequence divergence between representatives of several genera within the American lineage was significantly lower than that between the Eurasian Sedum species. Despite the relatively large number of sequences and their high divergence, we could not get a clear picture of relationships within the group because branching pattern of major clades and lineages of the tree remained largely unresolved. Perhaps further expansion of the taxon sampling in critical groups (Leucosedum and Eurasian cluster in "Acre" clade) will aid a more robust phylogeny of the subfamily.

© 2012 Organizing Committee