A new species of Psydrax (Vanguerieae, Rubiaceae) from the Gia Lai Plateau, southern Vietnam

Abstract A new species of Rubiaceae, Psydraxgialaiensis B.H.Quang, T.B.Tran & V.S.Dang, sp. nov., is described and illustrated from the Kon Chu Rang Nature Reserve, Gia Lai Province, southern Vietnam. This species is characterized by having strigose branches and leaves, a conspicuously bulging, short corolla tube, an accrescent nectary disc and a style with a dense tuft of hairs, which clearly distinguishes it from the other species in the genus. A description, vernacular name, conservation assessment, illustration, photographs, and a key to the species of Psydrax in Vietnam are provided.

During a botanical survey of the Gia Lai Province, southern Vietnam in 2017, specimens of the genus Psydrax were collected in a primary evergreen forest in the Kon Chu Rang Nature Reserve, at c. 1000 m elevation. After comparing with the specimens in the herbaria HN, MAK, KAG, and VNM, and specimen images on the website of JSTOR Global Plants (https://plants.jstor.org/), and consulting the relevant literature (Pitard 1924;Bridson 1985;Pham 2000;Reynolds and Henderson 2004;Chen et al. 2011), we determined that our specimens represent a new species.
Vernacular name. Căng gia lai Conservation status. Psydrax gialaiensis is commonly found in primary evergreen forests in the Kon Chu Rang Nature Reserve where it is well protected. Therefore, we suggest a status of Least Concern (LC) according to the IUCN Red List Categories (IUCN 2019).
Note. Psydrax gialaiensis is distinct from the other previously known species of Psydrax in Vietnam based on several characters mentioned in Table 1.

Discussion
Psydrax is distinguished from the other genera of tribe Vanguerieae represented in Vietnam by having leaves typically subcoriaceous to coriaceous, calyx limb truncate or 4-or 5-dentate, anthers completely exserted and usually reflexed, fruit obovoid and distinctly bilobed, as well as pyrene cartilaginous to woody with shallow apical crest (Bridson 1985;Cheek and Sonké 2004;Reynolds and Henderson 2004;Chen et al. 2011;Arriola and Alejandro 2013). The new species we collected in the Kon Chu Rang Nature Reserve is shown to be a member of the genus Psydrax because it is characterized by these features. However, it is unlike other species of Psydrax, which are usually entirely glabrous, the exception being P. maingayi (Hook.f.) Bridson and allied taxa (Malaya/Indonesia). This species has leaves that are finely pubescent beneath and straight-sided corolla tubes, whereas in P. gialaiensis the pubescence is strigose and the corolla tube conspicuously bulging. Especially, the new species is distinct in its style with a tuft of dense hairs, its accrescent disc and its pubescent anthers. Molecular phylogenetic studies on the new species are needed.
With three species of Psydrax reported in Vietnam, P. gialaiensis is the only species of the genus known from Kon Chu Rang Nature Reserve, Gia Lai Province. Unlike the habitat of the other three species, which occur in the secondary evergreen forest, evergreen mixed forest and along the edge of forests, P. gialaiensis is found only in primary evergreen forests.
Key to the species of Psydrax in Vietnam