Schizostachyum dakrongense (Poaceae, Bambusoideae), a new species from Dakrong Nature Reserve, Vietnam

Abstract Schizostachyum dakrongense is a new species of woody bamboo from Dakrong Nature Reserve, Quang Tri Province, central Vietnam. It is closely related to S. hainanense but differs by its pseudospikelets having terminal rachilla segments with ciliate margin and 6 bracts; culm sheath with the base of the outer margin having a slight projection below its point of attachment at the node, as well as sheath blades usually less than half as long as the culm sheath proper; and leaf blades pale-puberulent and sparsely pilosulous on the abaxial surface. The new species is described and illustrated here.

The first species of Schizostachyum in Vietnam was discovered by Balansa, who reported S. zollingeri Steud. (Balansa 1890). E.G. Camus also recorded this species in his monograph (Camus 1913). Several years later, E.G. Camus and A. Camus found another species of Schizostachyum in Vietnam, namely S. aciculare Gamble (Camus and Camus 1923). In 1942, McClure recorded two further species, S. pseudolima McClure and S. hainanense Merr. ex McClure (McClure 1942). Besides the above-mentioned four species, Pham recorded another seven species of Schizostachyum bamboo in Vietnam (Pham 2000). In the Bamboos of Vietnam, Nguyen increased this number to sixteen, with many undescribed species (Nguyen 2006). But after systematically researching Vietnam Schizostachyum, Tran (2011) thought that six species previously determined as Schizostachyum were in fact misidentifications. In his revision, he followed Xia's concept and recognized that there were fifteen species of Schizostachyum in Vietnam, including several undescribed ones.  (Tran et al. 2010(Tran et al. , 2013(Tran et al. , 2016. Dakrong Nature Reserve is located in Quang Tri province, central Vietnam. The main terrain of the reserve includes low ranges that are part of the Annamite Mountains. With a tropical monsoon climate, the average annual temperature of this area is 22−24 °C and the average annual precipitation is 2500−3000 mm. There are large areas of lowland forest in the reserve. These forests are located in a zone of overlap between the tropical Indo-Pacific/Sunda and subtropical/temperate China floristic regions. Consequently, this area shows high species richness and diversity (Trai et al. 1999). About 1053 species of plants are recorded for the 40,253 ha area (CRES 2005).
During a field survey in Dakrong Nature Reserve in November 2018, we collected a flowering bamboo which appeared similar to S. hainanense. But after further study, we confirmed that it is an undescribed species characterized by a ciliate margin in the terminal rachilla segment of the pseudospikelet and the base of the culm sheath's outer margin developing a slight projection below the point of attachment at the node.

Materials and methods
Material from this new species was collected from the type locality. Flowers were dissected under an Olympus-SZX16 microscope and photomicrographs microphotos were taken with a Qimaging MicroPublisher 3.3 RTV instrument. Morphological comparisons were based on characters recorded in the relevant literature including protologues, as well as a study of type specimens. The type specimens, photos and living plants were used for describing this new species. Diagnosis. This new species resembles Schizostachyum hainanense in having culm sheaths with an asymmetrically concave apex and well-developed oral setae. However, S. dakrongense differs from S. hainanense in its pseudospikelets having a terminal rachilla segment with ciliate margin, and 6 bracts; the base of the culm sheath outer margin with a slight projection below its point of attachment; culm sheath blades that are usually less than half as long as the sheath proper; pale-puberulent and sparsely pilosulous leaf blade abaxial surfaces.
Etymology. The species epithet "dakrongense" refers to the type locality: Dakrong Nature Reserve, Quang Tri Province, Vietnam.
Phenology. New shoots are found from summer to autumn. Distribution and habit. According to our investigations and the available data, S. dakrongense is only distributed in Dakrong Nature Reserve. It commonly occurs in evergreen forest at an elevation of ca. 200 m, together with Eurycoma longifolia Jack, Ficus hirta var. roxburghii King, Archidendron occultatum (Gagnep.) I.C. Nielsen, and a species of Ochna.
Conservation status. The species is found in a protected area, so its environment appears to be relatively stable. It is locally common. However, the area of distribution is less than 400 km 2 . According to International Union for Conservation of Nature (IUCN) Red List categories and criteria, this species should be treated as Endangered (EN) (IUCN 2012).