Cleisostoma Blume (1825: 362)

Averyanov, Leonid V., Nguyen, Van Canh, Vuong, Truong Ba, Quang, Bui Hong, Nguyen, Khang Sinh, Le, Tuan Anh, Binh, Tran Duc, Maisak, Tatiana V. & Nguyen, Cuong Huu, 2025, New orchids in the flora of Vietnam X (Orchidaceae, Orchidoideae, tribe Orchideae, Epidendroideae, tribes Gastrodieae, Arethuseae, Cymbidieae, and Vandeae), Phytotaxa 681 (1), pp. 20-54 : 38-41

Cleisostoma Blume (1825: 362) .

Cleisostoma nangongense Tsi (1989: 26 , fig. 3), Chen et al. 2009: 463, Xu et al. (2010: 634, 635, fig.625a & b), Zhou et al. (2016: 31), Jin et al. (2023: 695, figs. 76 & 77), not Kumar et al. (2020: 48, fig. 1 = C. schoenorchaefolium ). ( Fig. 9 & 10 )

Type:— China. Yunnan: Xishuangbanna (Mengla), 20 June 1985, Z. H.Tsi 215 (holotype PE, photo!).

Description (based on Vietnamese plants):—Epiphytic monopodial glabrous (except some details of flower) herb. Stem pendulous, rather slender, terete, simple or few branching to 0.6 m long, (1.5)2(2.5) mm in diameter, with internodes (1.6)2–3(3.4) cm long and many distant vermiform, roots, which often thicker than the stem. Leaves sessile, dark green, recurved or somewhat flexuose, semi-terete, adaxially channeled, (8)10–14(16) cm long, (1.8)2–2(2.2) mm in diameter, with a persistent sheathing base, acute without constriction near apex. Inflorescence pendent, lax raceme or panicle with 1–2 branches, bearing totally to 20 flowers; peduncle, greenish, heavily mottled with brown purple, bearing (2)3–4(5) minute, triangular, distant, sterile bracts; rachis longitudinally irregularly ribbed, (2.5)3–8(9) cm long, 1–1.2 mm in diameter. Pedicel and ovary olive green flushed with purple brown, terete, (3.5)4–6.5(7) mm long, 0.6–0.8(1) mm in diameter, longitudinally obscurely 6-grooved. Flowers widely opening, (0.7)0.8–1.2(1.3) cm across; petals and sepals spreading to bent backwards, dull yellowish-green with pale reddish-brown spots, 3-veined, with entire margin; lip light yellowish; anther cap yellow. Sepals subsimilar, narrowly obovate, (4.8)5–5.2(5.4) mm long, (2.4)2.6–3(3.2) mm wide, roundish at apex; median sepal slightly concave; lateral sepals slightly oblique, with strongly recurved margins. Petals narrowly obovate, slightly oblique, (3.8)4(4.2) mm long, (1.2)1.4–1.8(2) mm wide, roundish at apex, with somewhat recurved margins. Lip fleshy, 3-lobed, spurred, (7.8)8–9.2(9.4) mm long from apex of spur to apex of median lobe, 3.4–3.6 mm wide, adaxially finely papillulate; lateral lobes triangular, forward directed, 1.5–2.5 mm long and wide, acute; each lobe inside near apex with an prominent finger-like or subulate incurved processus and a prominent incurved wing-like semicircular flap near the base; median lobe triangular sagittate, fleshy, 1.8–2 mm long, (2.6)2.8–3.4(3.6) mm wide, spreading forwards, with 2 prominent broad suborbicular calli on adaxial surface, at base constricted, apex truncate; spur oblong, 5–5.5 mm long, 2–2.2 mm wide, backward directed, dorsiventrally flattened, below with shallow longitudinal groove, almost round at apex, inside with prominent incomplete septum and inverted V-shaped callus on the back wall of spur. Column stout, shortly cylindric, (2.6)2.8–3(3.4) mm tall, 2.4–2.8 mm wide, wingless, at base finely hairy; rostellum insignificant, in form of 2 flap-shaped rudiments. Operculum helmet-shaped, half-globular, (1.2)1.4–1.6(1.8) mm in diameter, with prominent obscurely quadrate, forward directed beak, truncate and somewhat notched at apex. Pollinia 4, subsimilar, half-globular, arranged in 2 units, bright yellow, held on apex of erect caudicle perpendicular to viscidium; viscidium collar-shaped, 1–1.2 mm wide; caudicle oblong, conduplicate, attached to top of viscidium, 0.9–1.1 mm long, almost straight or slightly back curved. Fruit cylindrical, slightly curved, shortly stalked, longitudinally 6-ridges capsule 1.7–2 cm long, 2–3 mm in diameter (not ripe).

Ecology and phenology (in Vietnam):—Epiphyte on mossy trees. Evergreen broad-leaved submontane forests on rocky limestone at elevations of 1000–1200 m a.s.l., very rare. Flowers in June–July.

Distribution: — Vietnam (Son La Province, Thuan Chau District). China (Yunnan Province, Xishuangbanna autonomous prefecture).

Conservation status:— Cleisostoma nangongense is presently known in Vietnam from a single location with one documented population, which area has no official protection and experienced currently the wide uncontrolled deforestation. This is inferred as continuing decline in quality of habitat. Based on the above information this species can be assessed as Critically Endangered B2ab(iii) following formal criteria proposed by the IUCN (2024). This species is also distributed in China where the conservation status is declared as Vulnerable ( Jin et al. 2023). There are chances of immigration of propagules from adjacent areas in north, hence, the preliminary assessment of CR is downlisted to Endangered [EN B2ab(iii)] fore regional assessment in Vietnam.

Notes:— Plants discovered in Vietnam almost entirely fit in their morphological characters with Cleisostoma nangongense described from SW Yunnan. Meanwhile, Vietnamese plant has entire, straight margin of sepals and petals in contrast of denticulate sepals and petals reported for Chinese plants ( Tsi 1989, Chen et al. 2009, Jin et al. 2023). If this observation is true, Vietnamese plants should be regarded as a separate variety.

From the other hand, Cleisostoma schoenorchaefolium Kumar & S.W.Gale in Kumar et al. (2018: 157, fig. 1 & 2) described from NW Laos (Type:—Lao PDR., Xayaboury Province: Parklai District, Mouang Pa Village, Pha Pheung Mountain, 30 June 2016, 455 m, Fischer, Kumar, Phaxaysombath & Sysouphanthong HNL-KFBG 0729) and regarded later as a synonym of C. nangongense ( Kumar & Gale 2020) it seems is actually a separate taxon. It differs from plants found in China and Vietnam in a series of following distinct characters: leaves to 24 cm long (vs. leaves 8–17 cm long, leaf apex with a constriction 1–1.5 cm before the tip (vs. leaves have no constriction near apex), inflorescence raceme with up to 5 (vs. inflorescence raceme or panicle with up to 20 flowers), sepals acute, 6–7.5 mm long (vs. sepals round at apex, 4.8–5.4 mm long), petals 2-veined, acute, 5–5.5 mm long (vs. petals 3-veined, round at apex, 3.8–4.2 mm long), lip 7.5–8.5 mm long from tip of spur to tip of median lobe (vs. lip 8.6–9.4 mm long), each lateral lobe inside near apex, with an inconspicuous triangular appendage (vs. appendage in form of prominent finger-like or subulate incurved uncinate processus), median lobe 2–2.3 mm long, 2.5–3 mm wide, slightly notched at apex (vs. median lobe 1.8–2 mm long, 3.4–3.6 mm wide, truncate), spur slightly scrotiform at apex (vs. spur apex almost round at apex), column 2.5 mm long, 2.5 mm wide (vs. column 3.4–3.6 mm tall, 2.8–3.2 mm wide), pollinia inequal, each unit comprising one larger and one smaller pollinium (vs. pollinia subequal, half-globular), caudicle strongly bent back, terminated in a prominent pointed hood (vs. caudicle straight or hardly bent back, distally without a pointed hood).

Both species differ from other congeners in sulcate leaves, but in floral morphology are very similar to C. chantaburiense Seidenfaden (1975: 70 , fig. 31) and C. simondii ( Gagnepain 1951: 628) Seidenfaden (1975: 66 , fig. 30) that do not support the segregation of C. schoenorchaefolium and C. nangongense into separate section, C. sect. Teretisculum Kumar & S.W.Gale in Kumar et al. (2018: 156).

Studied specimens: — Vietnam, Son La Province: Thuan Chau District, Chieng Pac Commune, pendulous, epiphyte on trunks or branches, in rocky mountain, 9 July 2023, Truong Ba Vuong, Nguyen Quoc Bao, BV1786 ( LE: LE 01253790https://en.herbariumle.ru/?t=occ&id=238798, LE 01276704https://en.herbariumle.ru/?t=occ&id=238799, LE 01253789, https://en.herbariumle.ru/?t=occ&id=238797 photos from plants prior preparation of voucher herbarium specimens BV1786 LE 01124283, https://en.herbariumle.ru/?t=occ&id=184044 LE 01255205 https://en.herbariumle. ru/?t=occ&id=239469).

Figures

FIGURE 9. Cleisostoma nangongense. A. Flattened wild-collected flowering plants. B. Leaf. C. Portion of leaf, adaxial side. D. Inflorescence. E. Distal portion of inflorescence. F. Flowers, views from different sides. G. Pedicel and ovary. H. Median sepal, adaxial and abaxial side. I. Lateral sepals, adaxial and abaxial side. J. Petals, abaxial and adaxial side. K. Lip, view from different sides. L. Column and lip, half-side view. M. Proximal part of lip, view from above. N. Sagittal section of lip and column. O. Column and lip, front view. P. Column apex with pollinarium, front and half-side view. Q. Column apex with pollinarium removed, front view. R. Back-wall callus, front view. S. Pollinarium, view from different sides. All photos by Truong Ba Vuong from the plant used for the preparation of voucher herbarium specimen BV1786. Photo correction and design by L. Averyanov and T. Maisak.

FIGURE 10. Cleisostoma nangongense. A.Flattened flower, frontview, operculumand pollinarium removed.B.Column with operculum, front view. C. Pedicel and ovary. D. Lip with spur dorsiventrally dissected. E, F. Lip dissected dorsiventrally, into part with side lobes (E) and part with median lobe (F). G. Lip, sagittal section. H–K. Operculum with pollinarium, view from below (H), from above (I), and side view (J, K). L–N. Pollinarium, rear view (L), front view (M), and side view, one pollinium separated (N).All photos by L.Averyanov from alcohol fixed plant used for the preparation of voucher herbarium specimen BV1786.