Cleisostoma mulunense Ying Qin & Yan Liu, sp. nov. (Figs. 1 & 2) Type:— CHINA. Guangxi: Huanjiang County, Mulun National Nature Reserve, elev. ca. 983 m, 27 July 2020, Yu-Lan Su ML2020001 (holotype IBK!; isotypes IBK!). Diagnosis:—The new species is close to C. menghaiense Z.H.Tsi (1983: 76), but it is easily distinguished from the latter mainly by its yellowish green to yellow, with purplish brown (vs. pale yellow with purplish red) flowers, suboblong (vs. elliptic) dorsal sepal, broadly oblong and obviously oblique (vs. obovate, slightly oblique) lateral sepals, oblong (vs. obliquely suboblong) petals, lip median lobe with (vs. without) 2 basal backward triangular lobules, cylindroid (vs. somewhat horn-shaped) spur. Herb epiphytic. Stem 2.0– 6.4 cm long, 2.6–3.7 mm in diameter, many-noded. Roots fleshy, 4.8–45.5 cm long, 1.5–4.1 mm in diameter. Leaves 6–13, distichous, linear, dorsiventrally compressed but convex between median vein and margin, slightly recurved, thickly fleshy, 3.4–6.5 cm long, 2.5–5.3 mm wide, margin entire, apex acute, base with amplexicaul-sheathing; median vein concave adaxially. Inflorescence axillary, 9.6–13.1 cm long, with 1–3 branches or unbranched, 20–41-flowered; peduncle 1.2–3.0 cm long, 0.8–1.3 mm in diameter, with 1–3 tubular sheaths; rachis slightly zig-zag curved, 6.8–10.1 cm long, 0.8–1.3 mm in diameter. Floral bracts triangular, acute, 0.6–1.5 mm long. Ovary terete, yellowish green, ca. 0.8 mm in diameter, including pedicel to 4.1–6.6 cm long. Sepals and petals yellowish green abaxially, purplish brown adaxially, margin yellowish green and denticulate, sometimes median vein yellowish green adaxially. Dorsal sepal suboblong, concave, 2.4–2.8 mm long, 1.5–1.9 mm wide, apex obtuse; lateral sepals broadly oblong, obviously oblique, 2.8–3.0 mm long, 1.8–2.2 mm wide, apex obtuse, base adnate to column foot. Petals oblong, 2.3–2.7 mm long, 1.2–1.4 mm wide, apex obtuse. Lip 3-lobed; lateral lobes broadly triangular, straight, slightly incurved at apex, yellowish green to yellow, 1.1–1.3 mm long, ca. 1.9 mm wide, proximal margin inflexed; median lobe triangular, slightly fleshy, yellowish green to yellow, with purplish brown apex, 2.7–3.2 mm long, 2.5–2.9 mm wide, base with 2 backward triangular lobules, apex acuminate and upcurved; disk with a longitudinal ridge extending from its center to spur mouth; spur yellowish green to yellow, cylindroid, dorsiventrally compressed, 3.9–4.2 mm long, 1.9–2.1 mm wide, slightly downcurved, concave on back wall at mouth outside, apex obtuse and with a tiny longitudinal septum inside, papillate at mouth inside, with a callus on back wall of mouth inside; callus nearly ligulatelinear, slightly widened from middle to upper part, papillate in lower part, with a central longitudinal groove. Column erect, stout, 2.0– 2.2 mm tall, 1.4–1.6 mm wide, yellowish green with purplish brown, papillate on front surface at base; column foot 1.7–1.9 mm long; stigma concave; pollinia 2, spherical, ca. 0.3 mm in diameter, each split into 2 subequal hemispheric portions, waxy, dark yellow, with a common stipe and a viscidium; stipe linear, slender, slightly widening near pollinia, ca. 1.1 mm long; viscidium elliptic, ca. 0.2 mm long; anther cap hemispherical, 0.8–1.0 mm in diameter, with a 0.4–0.6 mm long beak. Fruits unknown. Phenology: —Flowers in July and August. Etymology: —The epithet is derived from the type locality Mulun National Nature Reserve, Guangxi, China. Vernacular name: —ϮḖḆffi± (Chinese pinyin: mù lùn gé jù lán). Taxonomic notes:— Cleisostoma mulunense is close to C. menghaiense because of its short stem, linear and dorsiventrally compressed leaves with acute apexes, broadly triangular lateral lobes of lip. However, this new species is easily distinguished from the latter mainly by its yellowish green to yellow, with purplish brown flowers, suboblong dorsal sepal, broadly oblique-oblong lateral sepals, oblong petals, lip median lobe with 2 basal backward triangular lobules, cylindroid spur. Detailed comparisons between them are showed in Table 1. Distribution and ecology: — Cleisostoma mulunense is known only from the limestone areas of Mulun National Nature Reserve, Guangxi, China. This new species is an epiphytic plant on trees with an elevation of ca. 983 m. And it is companied by Platycarya strobilacea, Eriobotrya seguinii, Acer sycopseoides, Calocedrus rupestris, Sinosideroxylon pedunculatum, Quercus phillyreoides, Viola shiweii, Alyxia sinensis, Cymbidium floribundum, Luisia appressifolia, Paphiopedilum micranthum, Pholidota longipes, etc. Conservation status: —After many field surveys, only one population of Cleisostoma mulunense has been discovered with 73 mature individuals in Mulun National Nature Reserve. Its estimated area of occupancy is less than 10 km 2. And this species is mainly threatened by natural droughts, which cause death to some individuals. According to Guidelines for using the IUCN Red List Categories and Criteria (IUCN Standards and Petitions Committee, 2022), this species should be assessed as Critically Endangered [CR B2ab(V); C2a(ii)]. Additional specimens examined (paratype): — CHINA. Guangxi: Huanjiang County, Mulun National Nature Reserve, elev. ca. 983 m, 27 July 2023, Ying Qin GXQY20230727001 (IBK!).

Published as part of Qin, Ying, Tan, Wei Ning, Luo, Liu Juan & Liu, Yan, 2023, Cleisostoma mulunense (Orchidaceae), a new species from Guangxi, China, pp. 295-300 in Phytotaxa 616 (3) on pages 295-299, DOI: 10.11646/phytotaxa.616.3.9, http://zenodo.org/record/10146260