Ophiorrhiza guizhouensis (Rubiaceae), a new species from Guizhou Province, southwestern China

Abstract In this study, Ophiorrhiza guizhouensis, a new species of Rubiaceae from south-western China, is described and illustrated. The new species is morphologically similar to O. japonica, but differs from the latter by having terete stems which are densely hirtellous, usually persistent ciliate stipules with well-developed colleters inside the base of the stipule, shorter corolla tubes and shorter stamens and styles.


Introduction
Ophiorrhiza L. is a member of tribe Ophiorrhizeae, subfamily Rubioideae, Rubiaceae (Bremer and Eriksson 2009), including more than 300 species worldwide (WCSPF 2017). The genus is mainly distributed in wet tropical forests of South-East Asia, extending to Australia, New Guinea and the Pacific Islands (Darwin 1976, Chen andTaylor 2011). Ophiorrhiza is a taxonomically difficult genus and is poorly known in South-East Asia (Chen and Taylor 2011). In China, 68 species, including 47 endemics, are recorded (Chen and Taylor 2011, Deng and Huang 2012, Wu et al. 2017a and most of them are distributed in the region south of the Changjiang River, especially the provinces of Yunnan and Guangxi (Lo 1999).
During field work in north-eastern Guizhou, China, some specimens of Ophiorrhiza were collected. After carefully examining the specimens and living materials and reviewing the relevant literature (Lo 1990, 1999, Chen and Taylor 2011, it was concluded that the newly found plants represented an undescribed species. Here, the new species is described and illustrated.

Materials and methods
Specimens were collected during February 2017. Additionally, some flowers were also collected and preserved in FAA for subsequent observations. The photographs were taken in the field. Morphological observations and measurements of the new species were carried out based on living plants, dry specimens and preserved materials. Diagnosis. Similar to O. japonica Blume, but distinguished from the latter by the terete, densely hirtellous stems (vs. stems subterete to slightly compressed, glabrous or with 2 hirtellous or pilosulous lines), the usually persistent and ciliate stipules (vs. caducous glabrescent stipules), the well-developed colleters inside the base of stipule (vs. without colleters), the shorter corolla tubes (8-9 mm vs. 9-14 mm) and the shorter stamens and styles (longistylous flower: 2.5-2.7 mm and 7-8 mm vs. 4.5-5.5 mm and 9-11 mm; brevistylous flower: 3.6-4.2 mm and ca. 2.5 mm vs. 4.5-5 mm and ca. 3 mm).
Phenology. Plants were observed in full bloom on 19 February 2017. It can be expected that flowering time of the new species is from January to March; fruiting time needs further observations. Distribution and habitat. Ophiorrhiza guizhouensis is currently only known from Jiangkou County, Guizhou, south-western China, where at least 300 individuals are found. The species grows in evergreen broad-leaved forest or bamboo forest at elevations between 850-1,000 m, along with Chimonobambusa angustifolia C.D. Chu & C.S. Chao, Lindera communis Hemsl., L. pulcherrima var. hemsleyana (Diels) H.B. Cui, Clematis henryi Oliv. and Ophiopogon bodinieri H. Lév.
Etymology. The specific epithet refers to Guizhou, a province of south-western China in which the new species was collected.
Preliminary conservation status. The new species is currently only known from the type locality. More explorations are needed to fully understand its distribution and to assess its conservation status. Based on the available data, the new species is treated as "Data Deficient (DD)" according to the IUCN Red List Categories and Criteria guidelines (IUCN 2012).