Bulbophyllumchrysolabium (Orchidaceae, Epidendroideae, Malaxideae), a new species from Yunnan, China

Abstract Bulbophyllumchrysolabium, a new species belonging to section Racemosae from Yunnan, China is described and illustrated. The species is related to B.orientale and B.morphologorum, but differs by having the following set of characters: obliquely broadly-based triangular petals with a long filiform apex; lip densely glandular papillose and conspicuously ciliolate along margins; lip auricles well developed, narrowly falcate, tapering to a long sharp point at the apex; stelidia subulate and twisted inwards, slightly exceeding operculum. The conservation status of B.chrysolabium is assessed and taxonomic notes are provided.


Introduction
Recently, based on phylogenetic studies, all genera previously proposed in subtribe Bulbophyllinae were formally transferred to Bulbophyllum Thou. . As the largest orchid genus, Bulbophyllum Thou. (1822: tab. 93) is pantropical and widespread, with approximately 2200 species described worldwide (Sieder et al. 2007;. However, it is believed that there are still numerous species awaiting discovery and formal description. The high number of species in the genus Bulbophyllum makes systematic study not easy due to their morphological similarities and difficulties encountered in identifying them in their vegetative states. Bulbophyllum sect. Racemosae Benth. & Hk.f. (1883: 502) includes such species. According to the revised circumscription for section Racemosae (Seidenfaden 1979(Seidenfaden , 1992Vermeulen and O'Byrne 2011;, members of this section are characterized by distinct or well-developed pseudobulbs bearing a single leaf; inflorescence with many densely arranged flowers in a cylindrical raceme; mobile labellum usually with proximal auricles; distinct stelidia; basal node of pedicel approximately level with floral bract attachment. During our recent botanical survey in Menglian County of south-western Yunnan, China, an unusual species was discovered and collected. After further studies, the species was confidently classified as a Bulbophyllum species of section Racemosae, with approximately 38 species mainly distributed in tropical and subtropical Asia. There are seven species recorded in China, all of which occur in Yunnan Province (Seidenfaden 1979(Seidenfaden , 1992Tsi 1999;Li 2003;Chen and Vermeulen 2009;Ye and Li 2012;Averyanov et al. 2016). A thorough literature and herbarium specimen review indicated that it is clearly different from any other previously known taxon of the section.

Materials and method
Morphological comparisons and assessments of Bulbophyllum chrysolabium and its allies in the section Racemosae were performed based on specimens from herbaria BM, E, IBSC, K, KUN, PE (acronyms according to Thiers 2018), as well as consideration of the taxonomic literature. In addition, living plants were collected and transplanted to the nursery of the South China Botanical Garden, Chinese Academy of Sciences (SCBG) for further investigation. Measurements and photographs on the fresh material were made under a stereomicroscope (Olympus MD-90). The conservation status of the putative new species was evaluated following the guidelines of the International Union for Conservation of Nature (IUCN 2017).

Taxonomic description
Bulbophyllum chrysolabium L. Li & D.P. Ye, sp. nov. urn:lsid:ipni.org:names:77191936-1 Figures 1, 2 Diagnosis. Bulbophyllum chrysolabium is distinguished from all known congeners by having the following unique combination of features: obliquely broadly-based triangular petals with a long filiform apex; lip densely glandular papillose on both sides and conspicuously ciliolate along margins; lip auricles well developed, narrowly falcate, tapering to a long sharp point at the apex; stelidia subulate and twisted inwards, slightly exceeding operculum.
Taxonomic notes. Bulbophyllum chrysolabium appears to be related to B. orientale Seidenf. (Seidenfaden 1979: 138), especially in narrowly falcate lip auricles and twisted stelidia, but differs in distinctly longer floral bracts (almost twice as long as the pedicel and ovary); petals with long filiform apices, a rather smaller lip (ca. 2.8 mm long), significantly glandular-papillose and ciliolate at margins; stelidia slightly exceeding operculum and distinctly longer than column. With respect to filiform petals, B. chrysolabium is also superficially similar to B. morphologorum Kräenzl. (1908: 89), however, the latter have a fat, conical protuberance or callus on the front of the column near its base and scape much longer than rachis. In addition, it has subulate, not twisted stelidia, considerably longer than operculum; lip auricles not falcate, but rather obtuse at the apex. A detailed morphological comparison between B. chrysolabium and its allied species is presented in Table 1.
5-6 mm, nearly as long as or slightly longer than pedicel and ovary.
Scape 5-6 cm, rachis about 6.5 cm, longer than scape 10-13 cm, much longer than rachis Anther abaxially with a rounded crest, golden-yellow. Pollinia 4, the inner ones more than half as long as the outer ones. Distribution and habitat. So far known only from Menglian County in southwest Yunnan Province, China, growing as an epiphyte amongst mosses on the tree trunk near the edge of river in rather exposed circumstances in subtropical evergreen broad-leaved forest.
Etymology. The specific epithet comes from the Ancient Greek word chryso-"golden" and the Latin derived labium "labellum", referring to the golden-yellow lip of the type.
Phenology. Flowering observed in December. Conservation status. Bulbophyllum chrysolabium is known only from its type locality, where it is represented by a single population of about 30-50 individual plants or clumps. The extent of occurrence (EOO) of the species cannot be estimated and its area of occupancy (AOO) is estimated to be 4 km 2 , which falls within the thresholds for Critically Endangered under criterion B2. Additional individuals of this species may yet be found in adjacent areas as the investigation continues. The location is relatively inaccessible to casual hikers and the potential for habitat destruction is limited, but it is not in a national reserve or other kinds of protected areas. Fortunately, a few individuals were brought into cultivation at SCBG. Although there is limited data to determine its actual distribution range, biology and threats, the current available information (one location in a non-protected area and AOO less than 10 km 2 ) led us to assign a preliminary status of Critically Endangered [CR B2ab(iii)] according to the IUCN Red List Categories and Criteria (IUCN 2017).