The molecular phylogenetic position of Harpagocarpus (Polygonaceae) sheds new light on the infrageneric classification of Fagopyrum

In the context of the molecular phylogeny of Polygonaceae, the phylogenetic positions of most genera and their relationships have been resolved. However, the monotypic genus Harpagocarpus has never been included in any published molecular phylogenetic studies. In the present study, we adopt a two-step approach to confirm the phylogenetic placement of Harpagocarpus using two datasets: (1) a concatenated dataset of three chloroplast DNA (cpDNA) regions (matK, rbcL and trnL-F) for Polygonaceae and (2) a combined cpDNA dataset of five sequences (accD, matK, psbA-trnH, rbcL and trnL-F) for Fagopyrum. Our analyses confirm the previous hypothesis based on morphological, anatomical and palynological investigations that Harpagocarpus is congeneric with Fagopyrum and further reveal that H.snowdenii (≡ F.snowdenii) is sister to the woody buckwheat F.tibeticum. Within Fagopyrum, three highly supported clades were discovered and the first sectional classification was proposed to accommodate them: sect. Fagopyrum comprises the two domesticated common buckwheat (F.esculentum and F.tataricum) and their wild relatives (F.esculentumsubsp.ancestrale, F.homotropicum and F.dibotrys) which are characterised by having large corymbose inflorescences and achenes greatly exceeding the perianth; sect. Tibeticum, including F.snowdenii and F.tibeticum, is characterised by the achene having appurtenances along the ribs, greatly exceeding the perianth and the perianth accrescent in fruit; sect. Urophyllum contains all other species of which the achenes were completely enclosed in the perianth. This study is very helpful to understand the phylogeny of the Fagopyrum and sheds light on the future study of taxonomy, biogeography, diversification and character evolution of the genus.