Abstract
Abstract Orchidaceae, with 5 subfamilies, 22 tribes, 70 subtribes, 880 genera and 27, 000 species, is the largest family in flowering plants. Epidendroideae with 19 tribes, 39 subtribe, 576 genera and 15, 000 species, is the largest subfamily. Dendroibeae is the largest tribe in this subfamily and the second largest genus Dendrobium of Orchidaceae is located in this tribe. Dendrobium has 48 sections and 1, 400 species being classified. Among these sections, the sections Oxystophyllum (39 species) and Aporum (45 species) share the two following features: 1) wiry stem, fleshy and triangular sharp-pointed leaves are arranged in two ranks; 2) flowers are borne laterally from the apical region and usually form a cluster of chaffy bracts around the base of infloresence. Moreover, their distributions are overlapped from Myanmar to New Guinea. Thus, they were traditionally treated as closely related sections, with a slight difference in morphology: elongated terminal extension of the stem that lacks leaves and bears flowers in Aporum, but never appear in Oxystophyllum that bear one or two flower at a time and are formed in the leaf axils along the stem or apically. However, a previous study using molecular phylogeny with only two species of Oxystophyllum (O. govidjoae and O. sinuatum) and two species of subtribe Eriinae showed that Oxystophyllum should be moved from tribe Dendrobieae to the subtribe Eriinae in the tribe Podochileae. In this study, we analyzed this result by aligning two frequently employed phylogenetic marker genes, maturase coding gene (matK) in 4 Oxystophyllum species (O. minutigibbum, O. changjiangense, O. sp. Hainan* and O. sp. Sabah*) and other orchid 83 species and ribulose 1,5-biphosphatase large subunit (rbcL) in 3 Oxystophyllum species (O. minutigibbum, O. changjiangense and O. sp. Hainan*) and other orchid 57 species. The result shows that Oxystophyllum should be an independent genus and should be in tribe Podochileae. However, pollinia number comparison reveals that Oxystophyllum has four pollinia, which is different from the eight-pollinium character in subtribe Eriinae, and thus, we suggest that Oxystophyllum should not be in subtribe Eriinae.