Cleisostoma unisetum Aver. et Vuong

Cleisostoma unisetum Aver. et Vuong det. L. Averyanov at 10.2018  

Cleisostoma unisetum Aver. et Vuong; Photo Diep Dinh Quang

Vietnamese name: Miệng kín

Chinese Name:

Latin Name: Cleisostoma unisetum Aver. et Vuong

Family: Orchidaceae

Synonym Name:

Description:

The species epithet refers alone seta-like extension of the lip apex.

Description: Trunk and branch monopodial epiphyte. Stem simple, rigid, rugose wrinkled throughout, pendulous or spreading, (12)14–16(20) cm long, (4.5)5– 8(9) mm in diameter, with few wiry, straight to flexuose grey roots branching at apex; internodes (0.8)1–1.8(2.2) cm long. Leaves grassy green, glossy, sessile, dorsiventral, fleshy, rigid, spreading, almost perpendicular to stem, straight, conduplicate, oblong lanceolate, (6)8–14(16) cm long, (0.8)1–1.2(1.4) cm wide, with suddenly constricted, acute apex; leaf sheaths equitant, rigid, verruculose. Inflorescence lateral raceme (1.2)1.5–2(2.5) cm long, scape and rachis light grassy green; scape (4)5–8(10) mm long, straight, with (2)3–4(5) dark brown, persistent, triangular, acute, sterile bracts, (1.8)2–3(3.2) mm long and wide; rachis straight, thickened, angled, (0.8)1–1.5(1.8) cm long, with few to many spirally arranged, subdense flowers distant at (1)1.5–2(3) mm. Floral bracts minute, dark brown, triangular, acute, (1.4)1.5–2(2.2) mm long and wide. Pedicel and ovary dull pink to purple, perpendicular to rachis, (2.5)3–4(4.5) mm long, 1–1.2 mm in diameter, straight to slightly curved, terete, glabrous. Flowers widely opening, (6.5)7–8(8.5) mm across; sepals and petals rather fleshy, glabrous, spreading or median sepal somewhat forward curved; sepals inside pale yellow, outside brownish-purple with yellow apex; petals on both sides pale yellow with 1–2 more or less distinct dull purple stripes; lip lemon-yellow with white base; column white with purple apical half; anther cap yellowish speckled with purple; pollinia pale yellow. Sepals narrowly obovate, very concave, rounded or blunt at apex, (4.8)5–6(6.2) mm long, (2.2)2.4–2.6(2.8) mm wide; dorsal sepal hooded; lateral sepals slightly oblique. Petals oblong or narrowly obovate, rounded to blunt, as long as sepals, (1.7)1.8–2(2.1) mm wide, slightly oblique. Lip spurred, (5.8)6–6.5(7) mm long (from spur apex to the apex of median lobe), 3-lobed. Side lip lobes triangular oblique-falcate, more or less straight, vertical, forward directed, (1.5)1.6–1.8(2) mm long, 1.2–1.3 mm wide at the base, triangular-acute at apex. Median lip lobe fleshy, triangular sagittate, (2.4)2.5–2.7(2.8) mm long, (3.6)3.8–4.2(4.4) mm wide, obtuse, straight, forward directed, at apex attenuate into a single straight or upcurved slender filiform seta (0.9)1–1.2(2.3) mm long; at the base with transversal papillose ridge (connate with distal part of spur septum), disc along median line with three fleshy glabrous, prominent calli: basal callus conoid, somewhat forward curved, median callus half round, laterally flattened, apical callus conoid,  erect or somewhat forward directed, tooth-like; side lobules triangular, obtuse to acute, somewhat backward turned, 1.4–1.5 mm long. Spur short, broadly conoid, terete, parallel to column, (2.2)2.5–2.8(3) mm long, (2)2.2–2.4(2.6) mm wide, with almost round apex and incomplete glabrous longitudinal septum inside. Back- wall callus white, large, simple, rectangular, 1–1.2 mm long and tall, 0.6–0.8 mm wide, glossy smooth, at the base with lateral papillose arms spreading perpendicularly to lip margin. Column simple, shortly cylindrical, (2.6)3–3.5(3.8) mm high, 2–2.2 mm in diameter, with no wings; rostellum small, fleshy, bilobed, forward directed, furrowed longitudinally; stigma obscurely triangular to almost round. Anther cap hemispherical, (1.4)1.5–1.7(1.8) mm in diameter, with very short, insignificant beak. Pollinarium 1, with 2 pollinia, filiform stipe (tegula) 0.6–0.7 mm long and broad pliers-shaped viscidium, 1.2–1.4 mm broad. Pollinium ovoid, incompletely split into 2 subequal hemiovoid lobes. Fruits unknown. All measurements were taken from fresh and spirit material.
Flowering: Flowers blooming in July.

Distribution: In Vietnam: Khanh Hoa Province (Cam Lam District, Hon Ba Nature Reserve)

Ecological: at elevation about 1000 m a.s.l., evergreen broad-leaved submontane forest, epiphyte on tree trunk,

Note: Flower looks close to Cleisostoma striatum but only one hair on the tip of the lip, inflorescence short.

Reference:

- theplantlist.org

- efloras.org

- orchidspecies.com

- ipni.org

- Leonid V. AVERYANOV, Ba Vuong TRUONG2, Van Canh NGUYEN, Khang Sinh NGUYEN, Tatiana V. MAISAK; New Orchids (Orchidaceae) in the Flora of Vietnam II. Vandeae; Taiwania 64(3): 285-298, 2019