Molecular phylogeny of Atraphaxis and the woody Polygonum species (Polygonaceae): taxonomic implications based on molecular and morphological evidence

Abstract

The phylogenetic status of the genus Atraphaxis and its relationship with woody Polygonum species is examined based on nrDNA ITS and two chloroplast regions (matK and rpl32-trnL(UAG)). Morphological and palynological studies for the selected taxa are also performed. Our results revealed that several woody Polygonum species (namely P. spinosum, P. aridum, P. dumosum, P. salicornioides, P. khajeh-jamali and P. botuliforme) endemic to Iran formed a distinct clade, and are nested within Atraphaxis. Atraphaxis ovczinnikovii, (=P. ovczinnikovii), was the first diverging lineage as sister to an assemblage of these taxa and the bulk of Atraphaxis species. Three other woody Polygonum species (P. afghanicum, P. paronychioides and P. thymifolium) were nested within herbaceous Polygonum species. Ochrea and pollen characteristics corroborated the phylogenetic results as well. Based on molecular and morphological evidence, we transferred the aforementioned six Polygonum species into Atraphaxis. The newly delimited genus Atraphaxis is comprised of three lineages, corresponding to three new sections: Atraphaxis, Polygonoides and Ovczinnikovia. The different position of A. botuliformis (=P. botuliforme) in nrDNA ITS and combined chloroplast DNA analyses indicated that it had possibly experienced the hybrid or introgression for a long time. Taxonomic descriptions for Atraphaxis and its sections as well as the diagnostic key to sections and species occurring in Iran, are presented.