Hybridization and Chloroplast Captures in Asarum sect. Asiasarum (Aristolochiaceae) Documented by Chloroplast DNA Sequences
The phylogenetic relationships of Asarum sect. Asiasarum based on genetic variation in non-coding chloroplast DNA sequences were examined. A total of ca. 960 bp sequences of three non-coding regions, namely trnL (UAA) intron, rps16 intron and psbC-trnS (UGA) intergenic region, were analyzed for 37 accessions from 13 taxa and one geographic race. In the maximum-parsimony (MP) tree, four types were recognized. Among the 13 taxa and one geographic race, 10 taxa were identified as belonging to a single type, while the remaining three taxa and one geographic race, A. patens, A. sieboldii f. sieboldii, A. heterotropoides var. seoulense (from Korea) and A. versicolor, belonged to two types. The types all corresponded to more than one ribotype recognized in previous of nrDNA, ITS sequences. The phylogenetic tree topologies were difficult to compare. Chloroplast polymorphisms within a taxon and incongruence of the phylogenetic tree topologies between chloroplast and ITS were considered to be caused by chloroplast capture following hybridization. Reticulate evolution in sect. Asiasarum was therefore inferred to be more extensive than implied from ITS sequence data. Asarum maruyamae was speculated as being of hybrid origin from crosses between A. sieboldii f. sieboldii and A. mikuniense.