Spiradicliskarstana (Rubiaceae), a new species from Yunnan, China

Abstract Spiradicliskarstana, a new species of Spiradiclis (Rubiaceae) collected from Yunnan, China, is described for the first time. It is morphologically close to S.jingxiensis, but differs from the latter mainly by its inflorescences with 5–9 flowers, its 1.5–2.4 mm long peduncles, its stipules shorter than 1 mm and the 5–12 pairs of secondary veins. The conservation status is assessed as “Vulnerable” (VU) according to the IUCN Red List Categories and Criteria.


Introduction
Spiradiclis Blume, a small genus of Rubiaceae as currently circumscribed (Lo 1998(Lo , 1999, consists of two subgenera and ca. 50 species. Most of them are widely scattered in southern and south-western China and north-western India, but a few occur in the Indo-China Peninsula (Robbrecht 1988, Deb and Rout 1989, Lo 1999, Chen and Taylor 2011, Wu et al. 2015a, Wang 2016, Liu et al. 2017. Most representatives of the genus are narrowly distributed in karst regions, generally accompanied by ferns and Begonia L., Elatostema J.R.Forst. & G.Forst. and Gesneriaceae. During flowering, species of Spiradiclis are sometimes confused with Ophiorrhiza L. (Wu et al. 2015a), but they can be distinguished from the latter and other related genera by the linear-oblong or subglobose capsules that dehisce with four valves when mature (Lo 1999, Wu et al. 2015b. In China, nearly 47 species have been found, of which ten species have been published in the last four years (Deng et al. 2014, Wu et al. 2015a, Wang 2016, Liu et al. 2017. In 2017, a plant lover, Mr. Ming-Feng Long, found a population of Spiradiclis on the cliff of a karst hill in Malipo county, SE Yunnan and contacted the authors for the identification. The individuals were first identified as Spiradiclis jingxiensis R.J.Wang as they shared a similar habitat and morphological characters such as prostrate or decumbent habit, distylous and purple-reddish flowers with slender salverform corollas. After a further comparison of specimens, however, these individuals can be distinguished from Spiradiclis jingxiensis mainly by their puberulent to subglabrous stems, leaves, stipules, peduncles and calyces (vs. dense pubescence), their ovate-triangular stipules, shorter than 1 mm (vs. linear, 1.5-3.0 mm long), their elliptic to oblong leaf blades (vs. ovate to broadly ovate), their 5-12 pairs of secondary veins (vs. 4-5 pairs) and their inflorescences with 5-9 flowers (vs. 1-2 flowers). Therefore, the specimens are assumed to represent an undescribed new taxon, which is here described.

Materials and methods
Most materials are deposited at the herbarium of forest plants in the Central South University of Forestry and Technology (CSFI), only one residing at Guangxi Institute of Botany, Guangxi Zhuang Autonomous Region and Chinese Academy of Sciences (IBK). Morphological observations of the new species have been carried out, based on field observations as well as on dry specimens. The conservation status of the new species is evaluated in accordance with IUCN guidelines (2016). Diagnosis. Similar to S. jingxiensis, but differing from this species by the ovate-triangular stipules less than 1 mm long (vs. stipules linear, 1.5-3.0 mm long), the elliptic to oblong leaf blades (vs. ovate to broadly ovate), the 5-12 pairs of secondary veins (vs. 4-5 pairs) and the inflorescences with 5-9 flowers (vs. inflorescences with 1-2 flowers).
Phenology. Flowers and fruits were observed in April. We think flowering and fruiting may extend till May, because many flowers in April were still in bud.
Distribution and habitat. Spiradiclis karstana is known only from the crevices of forested cliffs at altitudes ranging from 800 to 1600 m in the karst area of SE Yunnan. This part of Yunnan is covered by evergreen rain forests that are highly similar to those in Indo-Malaysia (Zhu 2013) and are dominated by species from Magnoliaceae, Lauraceae, Dipterocarpaceae and Annonaceae.
Etymology Conservation status. So far, only two populations with about 300 individuals each have been found, notably near the towns of Mali and of Shuitian. The area of occupancy is estimated to be less than 4 km 2 . Despite the fact that only two populations with relatively few individuals are known, the status of Spiradiclis karstana is not pessimistic. It may count on the strong adaptability of the species to the severe habitat where interference from humans is usually weak and where it is very hard for people to reach and the efficient government policy to protect the local vegetation (Lai et al. 2000, Sui and Chen 2006, Zhu et al. 2007). Considering all of the above, this species is therefore assigned a status of "Vulnerable" [VU B2ab(ii,iii,iv)] according to the IUCN criteria (2016).

Discussion
Karst ecosystems are known to be distinctive in vegetation and biodiversity and have an extreme and exceptional habitat that can provide the opportunity for speciation and radiation (Myers et al. 2000, Zhu 2007, Biswas 2009). As mentioned above, most representatives of Spiradiclis prefer this unique ecosystem. It may be the reason why this small genus shows fairly complex and diverse habit and morphology.  (Sui and Chen 2006, Chen and Taylor 2011, Wu et al. 2015a, 2015b, Wang 2016). The following key is provided to the prostrate or decumbent Spiradiclis species worldwide.
A key to the prostrate or decumbent species in Spiradiclis. This key was adapted from Chen and Taylor (2011)