Vacciniummotuoense (Ericaceae), a new species from Xizang, China

Abstract Vacciniummotuoense (Ericaceae), a new species from Motuo County, Xizang Autonomous Region, China is described and illustrated. This new species belongs to Vacciniumsect.Calcicolus and is morphologically most similar to V.dunalianum, but differs in having yellowish-brown tomentose young branches, petioles and inflorescence rachis, leaf blades with 2–3(–4) pairs of secondary veins, usually all basal and with fine veins impressed adaxially and urceolate to spherical corollas.


Introduction
The genus Vaccinium L. (Ericaceae), with about 450-500 species distributed worldwide, is the largest genus of the blueberry tribe or Vaccinieae Rchb. (Fang 1991;Fang and Stevens 2005;Vander Kloet and Dickinson 2009 (Tong and Xia 2015;Tong et al. 2020Tong et al. , 2021. There are 15 species of Vaccinium recorded from Xizang Autonomous Region, most of which occur in the south to south-eastern part of that Province (Fang 1986).
During work on a revision of Vaccinium species from China, we observed that several specimens, identified as V. dunalianum var. urophyllum Rehder & E. H. Wilson from Motuo County, southeast Xizang, differ substantially from those from other places in China in the leaf blade with relatively long caudate apex and the yellowishbrown tomentose inflorescence rachis. Thus, we conducted two field trips to collect fresh flowering and fruiting material for further study. We found that, in addition to the difference in the indumentum on the inflorescence rachis noted by Fang (1991: 95), the population of V. dunalianum var. urophyllum from Motuo County could be further distinguished from other populations of that variety and, even, the entire species V. dunalianum Wight by the shape and venation of the leaf blade and the shape of the corolla. Thus, we concluded that the population of V. dunalianum var. urophyllum from Motuo represents a new species, described below.

Materials and methods
Fruiting and flowering material was collected from Motuo County, Xizang Autonomous Region, China during two field trips in January 2020 and May 2021. Descriptions were based on both living and dried collections, which were deposited at the Herbaria of the Institute of Botany, Chinese Academy of Sciences (PE), Kunming Institute of Botany, Chinese Academy of Sciences (KUN) and South China Botanical Garden, Chinese Academy of Sciences (IBSC). Measurements were performed with a ruler and small plant parts were observed and measured under a stereomicroscope (Mshot-MZ101). indumentum of leaf blade and the axillary racemose inflorescence, but distinguished by the yellowish-brown tomentose (vs. glabrous or brownish-white pubescent) young branches, petioles and inflorescence rachis, leaf blades with 2-3(-4) pairs (vs. 4-5) of secondary veins, usually all basal (vs. only lowermost 2-3 pairs basal), with veins impressed adaxially (vs. plane or slightly raised) and flowers with urceolate to spherical corollas (vs. broadly campanulate) (Table 1).
Conservation status. Vaccinium motuoense is common in the forests of Motuo County within an area over 3000 km 2 and the whole area is under the protection of Yarlung Zangbo Grand Canyon National Nature Reserve. The threat risk seems to be low because it is not economically valuable and the conservation condition of the Reserve is good. Thus, it is assigned a status of 'Least Concern' (

Discussion
According to Vander Kloet and Dickinson's infrageneric classification of Vaccinium, V. medongense fits well with the circumscription of V. sect. Calcicolus Kloet that is characterised by an evergreen habit, dimorphic perennating buds (i.e. floral perennating buds at least twice the size of vegetative perennating buds), racemose inflorescences with large caducous bracts, pseudo-10-locular ovary, berry with 2-5 seeds per locule and soft seed testa Dickinson 2005, 2009). In Xizang, besides V. dunalianum, there are two other species from the same section, viz. V. gaultheriifolium (Griff.) Hook. f. ex C. B. Clarke and V. glaucoalbum Hook. f. ex C. B. Clarke. However, these two species have glabrous and glaucous abaxial surface of leaf blades with serrate margins and acute or acuminate apices and, thus, are easily distinguishable from V. motuoense. This new species is common in its area of distribution, usually growing together with other epiphytic plants on tree trunks covered with mosses, such as orchids, ferns and some other ericaceous species like Agapetes praeclara C. Marquand, A. forrestii W. E. Evans, Vaccinium leucobotrys (Nutt.) G. Nicholson, V. retusum Hook. f. ex C. B. Clarke and V. kingdon-wardii Sleumer.