Keywords: Homalium, new species, Salicaceae, taxonomy, Vietnam, Vu Quang National Park
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). The genus is characterized by bisexual flowers 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 classified 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 Vietnam, 11 species of Homalium have been known: H. caryophyllaceum (Zoll. & Moritz) Benth., H. ceylanicum (Gardner) Benth. (synonym, H. balansae Gagnep., H. hainanense Gagnep.), H. cochinchinense (Lour.) Druce (synonym, H. digynum Gagnep., H. fagifolium (Lindl.) Benth.), H. dasyanthum (Turcz.) W. Theob. (synonym, H. griffithianum Kurz), H. dictyoneurum (Hance) Warb., H. grandiflorum Benth., H. mollissimum Merr., H. myriandrum Merr., H. petelotii Merr., H. phanerophlebium F. C. How & W. C. Ko, and H. tomentosum (Vent.) Benth. (Gagnepain 1921, Lescot 1970, Hô 1999, Yang and Zmarzty 2007). Here, we describe an additional species, H. glandulosum Tagane & V. H. Nguyen, from Vu Quang National Park, Ha Thinh Province, North Central Vietnam.
Vu Quang National Park covers an area of ca. 56,000 ha containing an elevation gradient of over 2,000 m, from 30 m in the lowlands to 2,286 m at the summit of Mt. Rao Co (Rào CÓ), on the border with Laos (Vu Quang National Park Management Board 2014: see Fig. 1). The vegetation is diverse along the elevational gradient and Kuznetsov (2001) described five 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 amplification and sequencing were performed according to published protocols (Kress et al. 2009, Dunning and Savolainen 2010, Toyama et al. 2015)..
Homalium glandulosum Tagane & V. H. Nguyen, sp. nov.
VIETNAM. Ha Tinh Province; Vu Quang National Park; along the trail to the summit; in hill forest, alt. 453 m, 18°16'25.3"N, 105°21'40.8"E, 25 July 2015, Tagane S., Yahara T., Toyama H., Nguyen N., Yang C. J. & Nguyen H. V3735 (holotype KYO!; isotypes BKF!, DLU!, FU!, NTU!, the herbarium of Vu Quang National Park!).
Figure 1.Homalium glandulosum Tagane & V. H. Nguyen
A habit B a flowering branch C abaxial leaf surface D bark E apical branch showing glandular stipules and leaf base F inflorescence G close up view of flowers.
Figure 2.Homalium glandulosum Tagane & V. H. Nguyen
A flowering branch B stipule and base of a leaf C bracteole D flower E longitudinal section of gynoecium.
The specific epithet ‘glandulosum’ reflects the existence of distinct glands, often stalked, on stipule, leaf base and bracts.