Homalium glandulosum (Salicaceae), a new species from Vu Quang National Park, North Central Vietnam

Abstract Homalium glandulosum Tagane & V. H. Nguyen, from Vu Quang National Park in northern Vietnam, is newly described. This species is characterized by distinct glands, often stalked, at the base of the lamina and along the margin of the stipules and bracteoles. Illustrations, DNA barcodes of the two regions of rbcL and matK, and a key to the species of Homalium in Vietnam are also provided.


Introduction
Homalium Jacq., with more than 150 species, is a genus of woody plants widely distributed in the tropics of the world, with the center of diversity in Southeast Asia and Madagascar (Sleumer 1954, 1973, Applequist 2013. Th e genus is characterized by bisexual fl owers with free petals and sepals, obconical calyx tube adnate to ovary in the lower part (i.e., semi-inferior ovary) and disk glands. It was previously classifi ed in Flacourtiaceae (e.g. Sleumer 1954, Lescot 1970, Sleumer 1985, Yang and Zmarzty 2007 or Homaliaceae (Gagnepain 1921), but Chase et al. (2002) included it in Salicaceae sensu lato based on phylogenetic analyses of plastid rbcL DNA data.
In  (Gagnepain 1921, Lescot 1970, Hô 1999, Yang and Zmarzty 2007 Fig. 1). Th e vegetation is diverse along the elevational gradient and Kuznetsov (2001) described fi ve major forest types: lowland forests (alt. 10-300 m), hill forest (alt. 300-1,000 m), medium montane forest (alt. 1,000-1,400 m), montane forest (alt. 1,400-1,900 m) and upper montane forest (alt. 1,900-2,100 m). From the national park, 1,678 species of vascular plants, 94 species of mammals, 315 species of birds, 58 species of reptiles and 31 species of amphibians, including many endemic and rare species, have been recorded, indicating that Vu Quang National Park is one of the centers of biodiversity in Vietnam (Eames et al. 2001, Tordoff et al. 2004, Vu Quang National Park Management Board 2014. During our botanical inventory in Vu Quang National Park in July 2015, we discovered a previously undescribed species of the genus Homalium. Here we describe the species as H. glandulosum, accompanied with illustrations, DNA barcodes of the two plastid regions rbcL and matK (CBOL Plant Working Group 2009), and a key to the species of Homalium in Vietnam. DNA amplifi cation and sequencing were performed according to published protocols (Kress et al. 2009, Dunning and Savolainen 2010, Toyama et al. 2015. Tagane  Diagnosis. Similar to H. petelotii Merr., but diff ering in having distinct glands, often stalked, at base of lamina and along margin of stipules and bracteoles, and spreading hairs on rachis of infl orescences, calyx tubes, sepals and petals (vs. glabrescent or only short appressed hairs in H. petelotii). Also, similar to H. cochinchinense (Lour.) Druce and H. mollissimum Merr. but distinguished from these two by the distinct glands mentioned above and very sparsely pubescent branches and petioles (vs. pubescent to densely pubescent).
Distribution. So far known only from the type locality. Etymology. Th e specifi c epithet 'glandulosum' refl ects the existence of distinct glands, often stalked, on stipule, leaf base and bracts.
Conservation status. Data Defi cient. Only one fl owering individual was found in a protected area of Vu Quang National Park. Further eff orts for fi nding additional individuals/populations are needed to evaluate its conservation status.
Note. In Vu Quang National Park, another species of Homalium, H. cochinchinense, occurs in lowland forest (e.g., alt. 70 m, 27 July 2015, Tagane et al. V3818 (BKF!, DLU!, FU!, NTU!, the herbarium of Vu Quang National Park!). Th e species is easily distinguished as in the above diagnosis and the following key.