Scientific name: Dendrobium thinhii Aver.
English name:
Vietnamese name: Hoàng thảo thịnh
Other name:

Stems few, arising from short rhizome, simple, cylindric to narrowly fusiform, 8-25 cm long, young leafy throughout, old leafless, glossy chestnut-brown. Leaves lanceolate to narrowly ovate, 3.5-10 cm long. Inflorescence short, lax (1)2-4-flowered raceme, arising from leafless stem. Flowers widely opening, 2.5-3 cm across, almost white, sepals and lip with violet margin, disk apically with yellow- brownish spot. Sepals narrowly ovate, 1.4-1.6 cm long, forming saccate mentum 2-3.5 mm long, 4.5-5 mm wide; petals narrowly ovate rhomboid, little smaller. Lip movable, recurved, 1-1.4 cm long, 7-10 mm wide, 3-lobed, at the base with hemispheric hollow 1-1.2 mm in diam.; median lobe triangular sparsely hairy; side lobes erect, semicircular; disc white-farinaceous, with glabrous green glossy callus at the center. Column erect, shortly cylindric, without distinct rostellum and stelidia; column foot glossy olive-brownish, much longer than the column, 5.5-7.5 mm long, forward curved. Anther cap simple, conical hemispheric, finely verruculose, about 2 mm tall and wide.

Type:

VIETNAM. Kon Tum province: Ngoc Linh Mountains, mountain evergreen forest at elevation about 1700 m a.s.l., 28 April 2015, D.P. Thinh, L.Averyanov, T.Maisak, N.V.Duy, AL 34 (holotype, LE!).

Perennial clustering sympodial epiphytic herb. Rhizome very short, rigid, semi-woody, simple or few branching, 0.5- 1(2) cm long, 1.5-2.5(3) mm in diam., with thin flexuose roots, in apical part covered by scarious, overlapping scales early disintegrating into papyraceous remnants, old part of rhizome almost naked, dark gray-brown, longitudinally irregularly wrinkled. Stems erect, many-noded, cylindric to narrowly fusiform, narrowing to the base and apex, straight to slightly flexuose or arching, (8)10-20(25) cm long, (3)4-6(8) cm in diam. at a middle, with several leaves in upper half, young enveloped by yellowish to dull yellow-greenish tubular leaf sheaths, old naked, glossy chestnut-brown, irregularly wrinkled; internodes cylindric or slightly swollen near the apex, (0.4)0.5-2.5(3) cm long. Leaves (5)6- 8(10), distichous, sessile, sheathed; sheath tubular, as long as internode, distinctly veined, completely disintegrating or remaining in form of insignificant fibrous remnants on second-year stems; leaf blade suberect, rather thin, broadly lanceolate to narrowly ovate, (3.5)4-8(10) cm long, (0.6)0.8-1.4(1.6) cm wide, obtuse and shortly unequally bilobulate at apex. Inflorescence arising from the upper part of leafless second-year stem, suberect, short, lax (1)2-3(4)-flowered raceme; scape and rachis green to olive-brownish, zig-zag curved, (0.8)1-2(3) cm long, 0.8-1(1.2) mm in diam. Scape bracts and floral bracts, whitish, scarious, oblong ovate, straight, cymbiform, obtuse to blunt, (3)4-6(7) mm long, (0.5)1-1.8(2) mm wide. Pedicel and ovary light green, glossy, glabrous, (1.6)1.8-2.4(2.6) cm long, straight and bent down at apex; ovary obconic, longitudinally grooved, (1.5)2-2.2(2.5) mm long; 1-1.2 mm in diam. at apex. Flowers horizontally spreading or pendulous, widely opening, very fragrant, almost entirely white, sepals with violet margin and violet median vein; lip violet along margin, disk with large yellow-brownish spot and dull green callus; column and anther cap pure white; column at the base and column foot glossy olive-brownish. Sepals widely spreading, narrowly ovate, obtuse, 1.4-1.6 cm long, 5-6 mm wide, lateral sepals at the base oblique broadening to 7-8 mm wide, forming short broad almost globular saccate mentum (2)2.5-3(3.5) mm long, 4.5-5 mm wide. Petals more or less forward directed, narrowly ovate rhomboid, little shorter and narrower than sepals. Lip more or less movable, conduplicate-concave and strongly recurved, being flattened broadly rhomboid, (1)1.2-1.3(1.4) cm long, (7)8-9(10) mm wide, 3-lobed, at the base with distinct hemispheric nectary hollow 1-1.2 mm in diam.; median lobe concave, triangular, acute, (5)5.5-6(6.5) mm long and wide; side lobes erect, embracing column, semicircular, 2-2.5 mm tall, 3.5-4.5 mm broad; disc near the base of median lobe sparsely hairy with long hairs, at the middle with erect, large, glossy-glabrous, obovate callus 3-4 mm long, 1.8-2(2.2) mm wide; other adaxial lip surface and base of callus covered by thick deposits of pure white, farinaceous, snow-like granular pseudopollen. Column erect, stout, shortly cylindric,(2)2.2-2.6(3) mm tall and wide, without distinct rostellum and stelidia, at front with large, concave stigma; column foot much longer than the column proper, thick, longitudinally concave, (5.5)6-7(7.5) mm long, 2.5-3(3.2) mm wide, forward curved. Anther cap simple, conical hemispheric, finely verruculose, about 2 mm tall and wide, at front with distinct longitudinal groove. Pollinia 4, in two pair, yellow, each pollinium oblong falcate, 1 mm long, 0.3 mm wide.

Etymology:Species epithet refers to the name of its discoverer, orchid enthusiast—Mr. Do Phu Thinh.

Habitat, phenology and conservation status:—Miniature branch and trunk epiphyte. Primary submontane and montane evergreen, broad-leaved forests on granite. 1700 m. Fl. April-May. Very rare. Estimated

IUCN Red List status—DD.

Distribution:—Vietnam: Kon Tum province (Ngoc Linh Mountains). Endemic.

Notes:—This new species belongs to distinct group of Dendrobium species historically known as a section Breviflores (Hooker 1890: 711), but it is totally different from all known species of this section, as well as from other its congeners. Snow-like pseudopollen deposits on the lip, large glabrous callus on the disc and other specific lip structures are the most obvious individual features of this remarkable novelty species. Flowers of this plant have a very pleasant, extremely strong fragrance when fresh and surprisingly remaining even in completely dried herbarium samples. Formation of pseudopollen in flowers of this species is evolutionarily expressed to a greater extent than in any other orchid species in Indochina. It is remarkable that this species grows in the region of Dendrobium farinatum Schildhauer & Schraut (2004: 374) and D. unicum Seidenfaden (1970: 332), two other local endemics of eastern Indochina forming pseudopollen. The formation of pseudopollen is a rather rare phenomenon and coexistence of these three species may indicate regional and specific traits of pollination evolution in their overlapping distribution area.