Dendrobium khanhii Aver. & V.C.Nguyen

Averyanov, Leonid V., Nguyen, Van Canh, Vuong, Truong Ba, Nuraliev, Maxim S., Nguyen, Khang Sinh, Maisak, Tatiana V., Yudova, Daria A., Saidov, Nikita T., Nguyen, Cuong Huu & Nong, Duy Van, 2024, New orchids in the flora of Vietnam VIII (Orchidaceae: Epidendroideae, tribes Malaxideae, Neottieae and Podochileae), Phytotaxa 658 (1), pp. 1-49 : 27-29

Dendrobium khanhii Aver. & V.C.Nguyen , sp. nov.

( Fig. 13 )

Diagnosis: —The new species is morphologically most close to D. khanhoaense , from which it differs in glabrous leaves and leaf sheaths, pure white sepals and petals, light yellow greenish to yellowish lip, sepals 2–2.6 cm long and 7.2–8.4 mm wide, petals ellipsoid to narrowly ovate, 1.6–2.2 cm long and 7.2–8.7 mm wide (as wide as sepals), lip 2.1–2.5 cm long and 1.4–1.8 cm wide with narrowly conoid spur 9–11.5 mm long, epichile rectangular broadly obcordate, 7 mm long and 12–13 mm wide (as wide as hypochile), and white anther cap with purple apex.

Type: — VIETNAM. Quang Ngai Province: evergreen broad-leaved forest, at 1000–1500 m a.s.l., 15 August 2018, Van Khanh Nguyen, Van Canh Nguyen, AL 409 (holotype LE LE 01169571! https://en.herbariumle.ru/?t=occ&id=144139, photos of plant used for preparation of the type herbarium specimen LE LE 01124832 https://en.herbariumle.ru/?t=occ&id=219536).

Etymology: —The species is named after its discoverer, Mr. Nguyen Van Khanh.

Description:—Epiphytic herb with few suberect or pendulous stems densely clustering on short plagiotropic rhizome. Stem rigid, terete, slightly succulent, to (30)35–45(55) cm long, (4)4.5–5.5(6.5) mm in diameter, glabrous; young stems leafy throughout; old stems with few leaves or leafless, naked or with remaining leaf sheaths, yellow green. Leaves sub-distichous, sessile, grassy green, entirely glabrous, sheathed at the base; sheaths tubular, dull pale yellowish green; leaf blade oblong broadly lanceolate, (3)3.5–4.5(5) cm long, (0.6)0.8–1.4(1.6) cm wide, obtuse and unequally bilobed at apex, conduplicate with prominent median vein. Inflorescence arising laterally on leafless stem, with 1–2 flowers; peduncle dull greenish, (3)3.5–4(5) mm long, glabrous; floral bracts scarious, whitish, very small, glabrous. Pedicel and ovary not resupinate, terete, slightly to prominently curved, yellowish to dull orange, (1.8)2– 2.2(2.4) cm long, glabrous; pedicel about 1.2 mm in diameter; ovary 2.5–3.5 mm in diameter. Flowers widely opening, of thick texture, entirely glabrous. Sepals oblong narrowly ovate, pure white, (2)2.2–2.4(2.6) cm long, (7.2)7.4–8.2(8.4) mm wide, acute to shortly acuminate at apex; lateral sepals slightly oblique at base. Petals ellipsoid to narrowly ovate, pure white, (1.6)1.8–2(2.2) cm long, (7.2)7.5–8.5(8.7) mm wide, acute to shortly acuminate at apex. Lip obpandurate in outline, light yellow greenish to yellowish with white margin of epichile, with yellow disk, (2.1)2.2–2.4(2.5) cm long, (1.4)1.5–1.7(1.8) cm wide, at base attenuate and bearing narrowly conoid spur (9)9.5–11(11.5) mm long, 2.5–3.5 mm wide at base; side lobes half obovate, 1.1–1.2 cm long, 5.5–6.5 mm wide, slightly undulate at margin; median lobe (epichile) rectangular broadly obcordate, about 7 mm long, 12–13 mm wide, obscurely emarginate, strongly undulate along margin; disk at base of epichile with 3 low, distinct, slightly verrucose, bright yellow longitudinal keels. Column erect, stout, light greenish to almost white, 4.6–5 mm tall, 3.2–3.6 mm wide; column foot 5.6–5.7 mm long, 2.1–2.3 mm wide, straight, down directed; anther cap mitriform, white, with truncate purple apex, 2.2–2.4 mm tall, 2–2.2 mm wide, finely papillose. Fruits unknown.

Habitat and phenology: —Clustering epiphyte. Primary and secondary evergreen broad-leaved forests at elevations of 1000–1700 m a.s.l. Very rare. Flowers in March–August (under cultivation).

Distribution: —Endemic to S Vietnam: provinces Quang Nam (sine loc.) and Kon Tum (Ngoc Linh Mountains).

Conservation status: — Dendrobium khanhii is known in two localities in the area associated with the Ngoc Linh Mountains, at each side of the border between Kon Tum and Quang Nam provinces of Vietnam. Due to the deficiency of the available information on the species populations, we estimate the conservation status of this species as Data Deficient (DD). At the same time, the species possibly stands on the verge of extinction in nature due to vast deforestation in its known area of occupancy.

Notes: — Dendrobium khanhii clearly differs morphologically from all the other species of D. sect. Distichophyllum due to its large plant size, large white flowers, and broad petals. The new species is most similar in its morphology to another Vietnamese endemic, D. khanhoaense Averyanov (1999: 216) . Dendrobium khanhii differs from the latter species in glabrous (vs. bearing scattered fine black hairs) leaves and leaf sheaths, pure white sepals and petals (vs. sepals and petals white to yellowish with contrasting network of yellow brown veins), lip light yellow greenish to yellowish with white margin of epichile and yellow disk (vs. lip white, side lobes white with distinct yellow brown veins, epichile entirely orange brown), sepals 2–2.6 cm long, 7.2–8.4 mm wide (vs. 8–11 mm long, 4–5 mm wide), petals ellipsoid to narrowly ovate, as wide as sepals, 1.6–2.2 cm long, 7.2–8.7 mm wide (vs. lanceolate, twice narrower than sepals, 9–10 mm long, 1.5–2 mm wide), lip 2.1–2.5 cm long, 1.4–1.8 cm wide (vs. 1.3–1.5 cm long, 1.2–1.3 cm wide), spur narrowly conoid, 9–11.5 mm long (vs. broadly conoid, 4–5 mm long), median lobe of lip (epichile) rectangular broadly obcordate, 7 mm long, 12–13 mm wide, as wide as hypochile (vs. obreniform or bilobed, 3–4 mm long, 6–7 mm wide, much narrower than hypochile), anther cap white, with purple apex (entirely dark purple).

Additional specimen studied (paratype):— VIETNAM. Kon Tum Province: Living plant collected in Ngoc Linh Mountains, evergreen broad-leaved forest at elevation 1500–1700 m a.s.l., October 2017, Nguyen Van Canh, s.n., flowered under cultivation on 15 March 2024, L. Averyanov, AL1698 (LE LE01254649 https://en.herbariumle. ru/?t=occ&id=219268).

Figures

FIGURE 13. Dendrobium khanhii. A. Leafy shoots and flowering leafless shoots. B. Apical part of flowering shoot with inflorescence. C. Inflorescences. D–F. Flowers, view from different sides. G. Flattened sepals, petals and lip, adaxial side. H. Flattened lip, adaxial side. I. Disk of the lip, showing keels. J. Column, half-side view. K, L. Anther cap, front and rear view. M. Pollinia. Photos by Van Canh Nguyen from living plant prior to the preparation of the type herbarium specimen Nguyen Van Khanh, Van Canh Nguyen, AL409. Photo correction and design by L. Averyanov and T. Maisak.