Molecular Phylogeny of Tribe Atraphaxideae (Polygonaceae) Evidenced from Five cpDNA Genes

Polygonaceae, in general, has two recognized subfamilies, Polygonoideae and Eriogonoideae. Subfamily Polygonoideae has five tribes, however, the tribal classification within this subfamily is under dispute. Chinese researchers established the new Atraphaxideae genus (Parapteropyrum) from Tibet, China. At present, the tribe Atraphaxideae, according to the most widely accepted taxonomy, consists of Atraphaxis, Calligonum, Pteropyrum, and Parapteropyrum. Recently, sequence data has revealed that this tribe is not monophyletic.

The previous molecular phylogenies, mainly focusing on higher taxonomic levels, have omitted Parapteropyrum, and have lacked adequate Atraphaxis samples. Considering the disagreement over relationships in Atraphaxideae, Prof. ZHANG Mingli and his student examined the structure of the tribe by adding more taxa and sequences to further test the monophyly of Atraphaxideae, investigate the diversification of the four Atraphaxideae genera, and present a preliminary molecular phylogeny of Atraphaxis and Calligonum in China. Five chloroplast genes, atpB-rbcL, psbA-trnH, trnL–trnF, psbK-psbI, and rbcL of Atraphaxis, Calligonum, Pteropyrum, and Parapteropyrum were sequenced. The non-monophyly of Atraphaxideae was confirmed. Atraphaxis and Calligonum, respectively, formed a monophyletic group that was well supported.

The result showed that Calligonum is closely related to Pteropyrum; Atraphaxis is sister to Polygonum s. str.; and Parapteropyrum is allied with Fagopyrum. Although the morphology suggested the four genera should form a tribe, the molecular data indicated Atraphaxideae was not one monophyletic group. The clades identified within Atraphaxis corresponded well with the current sectional classification based on morphological features. As for Calligonum, Medusa was identified as a non-monophyletic section.

The result has been published on Journal of Arid Land, 2012, 4(2): 180–190. The paper is also archived at http://jal.xjegi.com/EN/abstract/abstract138.shtml.