Cleisostoma truongquanii Aver. & Vuong, 2025

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 : 41-44

Cleisostoma truongquanii Aver. & Vuong , sp. nov.

( Fig. 11 & 12 )

Diagnosis: — Cleisostoma truongquanii differs from morphologically closest C. dorsisacculatum in shorter leaves 4–7 cm long, inflorescence raceme or panicle with 1–5 branches, peduncle 3–4 cm long, twice smaller flowers 4–5.2 mm across, lip lobes without ornamentation, median lip lobe triangular sagittate, spur at entrance finely papillulate, inside without septum, and back-wall callus in form of very small, hardly visible pocket.

Type: — VIETNAM. Kon Tum Province: the border area between Tu Mo Rong and Dak Glei districts, Ngoc Linh Mountains, evergreen broad-leaved forest on granite at elevation of about 1700 m a.s.l., 22 July 2023, Truong Ba Vuong, Nguyen Ta Ton, BV1894. (holotype LE: LE 01277102 https://en.herbariumle.ru/?t=occ&id=242537, isotype LE 01276711 https://en.herbariumle.ru/?t=occ&id=238805, photos of plants used for preparation of herbarium type specimen LE: LE 01124284 https://en.herbariumle.ru/?t=occ&id=184043, LE 01255206 https://en.herbariumle.ru/?t=occ&id=237794).

Description: —Epiphytic monopodial glabrous herb. Stem erect to suberect, rather stout, terete, simple or few branching near the base, to 15–25 cm long, (5.5)6–7(8) mm in diameter, with internodes (0.8)1–1.6(2.4) cm long and several vermiform roots near the base. Leaves sessile, dark green above, light green below, rigid, distinctly conduplicate, slightly recurved to almost straight, oblong lorate, (4)4.5–6.5(7) cm long, (0.8)1–1.2(1.4) cm wide, with a persistent, greenish or brownish purple sheathing base and apex with two subequal roundish lobes. Inflorescence arcuate, sub-lax raceme or few branching many-flowered panicle; peduncle, 3–4(5) cm long, greenish, sometime with light purple tint, bearing (1) 2–3 minute, distant, triangular, sterile bracts; rachis longitudinally irregularly ribbed, to 6(7) cm long, 1.2– 1.4 mm in diameter; floral bracts triangular, insignificant, less than 1 mm long. Pedicel and ovary light green, slightly curved, terete, (1.8)2–2.8(3) mm long, about 0.5–0.7 mm in diameter, longitudinally obscurely 6-grooved. Flowers widely opening, (4)4.2–5(5.2) mm across; petals and sepals spreading, orange brown to purple brown with dull yellow margin, with entire margin; lip white with purple side; column light yellow with purple base, anther cap white to yellowish. Sepals subsimilar, 3-nerved, narrowly ovate to ovate, (2)2.2–2.5(2.7) mm long, (1.2)1.4–1.8(2) mm wide, obtuse; median sepal slightly concave, cucullate; lateral sepals slightly oblique. Petals narrowly oblong ovate, slightly oblique, (1.7)1.8–2(2.1) mm long, 0.8–1 mm wide, obtuse, almost flat. Lip fleshy, 3-lobed, spurred, (3.4)3.8–4.2(4.5) mm long from apex of spur to apex of median lobe, (1.4)1.6–1.8(2) mm wide; side lobes triangular, forward directed, (0.9)1(1.1) mm long and wide, acute; inside flat, without ornamentation; median lobe triangular sagittate, fleshy, 1.9–2 mm long and wide; side lobules acute, back directed; median lobule roundish to truncate, forward directed; spur obovoid saccate, 2–2.5 mm long, 1.8–2 mm wide, inside at entrance finely papillulate, very fleshy and strongly bent down at base, slightly dorsiventrally flattened, half globular at apex, inside without septum, back-wall callus in form of two insignificant folds united together and forming small pocket below column base. Column stout, shortly cylindric, 1–1.2 mm tall, 0.8–1 mm wide, wingless, at base finely papillulate; rostellum in form of two prominent, white, forward directed dents. Operculum helmet-shaped, half-globular, 0.7–0.8 mm in diameter, with prominent triangular, forward directed beak, obtuse to truncate at apex. Pollinia 4, subsimilar, half-ovoid, arranged in 2 units, bright yellow, held on apex of erect, narrowly oblanceolate stipe 0.5–0.6 mm long, placed almost perpendicular to plate-shaped bifid viscidium, ovate in outline 0.3–0.4 mm long, 0.15–0.2 mm wide. Fruits not seen.

Etymology: —The species epithet refers to the names of two sons of Mr. Nguyen Ta Ton, Truong (Nguyễn Phan Trường) and Quan (Nguyễn Trung Quân) who found and kindly provided the materials for this study.

Ecology and phenology:— Epiphyte on mossy trees. Evergreen broad-leaved montane forests on granite at elevations of about 1700 m a.s.l., very rare. Flowers in July.

Distribution:— Vietnam (Kon Tum Province, Tu Mo Rong and Dak Glei districts), endemic of Ngoc Linh Mountains.

Conservation status:— Cleisostoma truongquanii is presently known from a single location in Ngoc Linh Mountains 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. Accordingly, the one site of occurrence of this species is counted as 1 location. The AOO is estimated to be less than 10 km 2.The species is thus assessed globally as Critically Endangered B2ab(iii) following formal criteria proposed by the IUCN (2024).

Note:— Cleisostoma truongquanii in its morphology is most close to C. dorsisacculatum Aver. in Averyanov et al. (2016: 330, fig. 6D-G & 7) sharing rather similar plant habit, shape and color scheme of flowers, and pocket-like back-wall callus. At the same time our new species differs in many characters, such as leaves 4–7 cm long (vs. leaves 6–14 cm long), inflorescence raceme or panicle with 1–4(5) branches and peduncle 3–4 cm long (vs. inflorescence panicle with 4–14 branches and peduncle 10–18 cm long), pedicel and ovary 1.8–3 mm long (vs. pedicel and ovary 4–6 mm long), flowers 4–5.2 mm across (vs. flowers 6–7.5 mm across), sepals 2–2.7 mm long (vs. sepals 3.2–3.8 mm long), petals 1.7–2.1 mm long (vs. petals 3.2–3.8 mm long), lip 3.4–4.5 mm long from apex of spur to apex of median lobe (vs. lip 4.2–5 mm long), side lobes triangular 0.9–1.1 mm long and wide, inside flat, without ornamentation (vs. side lobes narrowly triangular, 1.1–1.5 mm long, 0.5–0.6 mm wide, inside with enrolled fold and prominent papillose callus), median lobe triangular sagittate, 1.9–2 mm long and wide; side lobules acute, back directed; median lobule roundish to truncate, disc without ornamentation (vs. median lobe triangular 1.2–1.6 mm long, 1.6–2.2 mm wide, at apex blunt to roundish or subtruncate, disc with 2 prominent papillose inflations), spur 2–2.5 mm long, 1.8–2 mm wide, inside at entrance finely papillulate, slightly dorsiventrally flattened, inside without septum (vs. spur 2.8–3.4 mm long, 2–2.6 wide, inside almost glabrous, dorsally strongly concave, inside with distinct incomplete septum), back-wall callus in form of two insignificant folds united together and forming very small glabrous pocket below column base (vs. back-wall callus in form of large, half-ovoid, finely papillose container 2–2.2 mm long, 1.6–1.8 mm wide, swelling during anthesis and sometimes opening with age at apex by two narrow lateral splits), column 1–1.2 mm tall, 0.8–1 mm wide (vs. column 1.6–2.2 mm high, 2.4–2.6 mm wide), anther 0.7–0.8 mm in diameter (vs. anther cap 0.9–1 mm in diameter), and pollinarium stipe 0.5–0.6 mm long with viscidium 3– 0.4 mm long (vs. stipe 0.8–1 mm long, with viscidium 0.35–0.45 mm long).

Both species are reported from similar habitats of Central Highlands in southern Vietnam. Meanwhile, flowering of C. truongquanii is observed in July, when C. dorsisacculatum flowers in November.

Figures

FIGURE 11.Cleisostoma truongquanii.A.Flattened wild-collected flowering plant.B.Intactinflorescence.C–D. Portionofinflorescence. E. Flowers, views from different sides. F. Median sepal, adaxial and abaxial side. G. Lateral sepals, adaxial and abaxial side. H. Petals, adaxial and abaxial side. I. Lip, side view. M. Dorsiventral section of spur. N–O. Cross section of spur. P. Column, side and front views. Q. Operculum, view from above and from bottom. R. Pollinaria, views from different sides. All photos by Truong Ba Vuong from the plant used for the preparation of the holotype specimen BV1894. Photo correction and design by L. Averyanov and T. Maisak.

FIGURE 12. Cleisostoma truongquanii. A. Flattened flower, front view. B. Flower, back view. C. Pedicel and ovary. D. Flower with dorsiventrally dissected and artificially recurved spur. E. Lip and dorsiventral section of spur. F. Flower with dorsiventral section of spur, showing backwall callus. G. Back-wall callus. H. Sagittal section of the lip. I. Column with intact anther, side view. J–L. Column, side view (J), front (K), and rear view (L). M. Column, front view, showing intact anther and viscidium. N. Column with artificially recurved operculum and pollinarium, side view. O, P. Operculum with pollinarium, view from top (O), and from bottom (P). Q. Operculum with pollinia and artificially recurved stipe. All photos by L. Averyanov from alcohol fixed plant used for the preparation of the holotype specimen BV1894.