Phylogeny and Systematics of the Bistorta manshuriensis complex (Polygonaceae)

Abstract

The Bistorta manshuriensis species complex consists of closely related and morphologically variable five taxa distributed in northeast Asia including Russia Far East, North East China, Korea and Japan. Taxonomic identity and species delimitations have been problematic in the complex. To delimit species boundaries, and to clarify taxonomic postion and phylogenetic relationships within the B. manshuriensis complex, major morphological characters were examined and DNA sequences were analyzed. The results of morphological analyses show that the length and width of leaf blade, position of maximum width in the leaf blade ratio between length and width of leaf blade, length of petiole wing are useful characteristics in distinguishing the taxa of the complex. Somatic chromosome counts revealed diploids (2n = 24) and tetraploids (2n = 48) in the complex. The chromosome counts reported herein represented the first reports for B. manshuriensis and B. alopecuroides. Variations in ITS and cpDNA regions were examined in 182 accessions sampled from 82 populations from almost the entire distribution area of the taxa of the B. manshuriensis complex. Twenty eight ribotypes were identified on the basis of 22 substitutions and one indel in the ITS. Ribotype polymorphism was prevalent in all taxa of the complex. in the majority of populations. A geographically widespread ribotype was detected in all populations examined except two populations in Korea. Among 28 ribotypes, eight were shared by two or more taxa of the complex and thirteen ribotypes were population-specific. Forty three haplotypes were identified on the bases of 64 nucleotide substitutions and 1 indel in the combined cpDNA sequence data. Eight haplotypes were shared by two or more taxa of the complex, and twenty seven haplotypes were population-specific. A geographically widespread haplotype distributed in 34 populations was detected in the complex. TCS haplotype network and phylogenetic tree analyses inferred from the combined cpDNA sequence data indicated several lineages in the complex. However, no lineage corresponded to the currently recognized delimitations of taxa. Based on nuclear rDNA ITS and cpDNA phylogenetic analysis as well as TCS network analysis, it is concluded that the speciation in the B. manshuriensis complex involved the complex pattern of hybridization, incomplete lineage sorting, mutations and geographical divergence.