Description from Flora of China
Callista longicornu (Lindley) Kuntze; Dendrobium bulleyi Rolfe; D. flexuosum Griffith; D. hirsutum Griffith; D. longicornu var. hirsutum (Griffith) J. D. Hooker.
Stems clustered, pendulous, cylindric, 7-35 cm, 2-4 mm in diam., slightly rigid, unbranched, with many nodes, internodes 2-4 cm. Leaves several, narrowly lanceolate, 3-7 × 0.5-1.4(or more) cm, leathery, both surfaces and leaf sheaths with blackish brown rigid hairs, base decurrent forming clasping sheaths, apex acuminate, unequally laterally bilobed. Inflorescence subterminal, 1-3-flowered; peduncle ca. 5 mm; basal sheaths 3 or 4, 2-5 mm; floral bracts ovate-lanceolate, 5-8 mm, abaxially dark brown hairy, apex acute. Pedicel and ovary nearly cylindric, 2.5-3.5 cm. Flowers pendulous, pointing downward, cylindric, white, lip with central part of disk orange. Dorsal sepal ovate, 15-20 × ca. 7 mm, 7-veined, midvein slightly keeled abaxially, apex acute; lateral sepals obliquely ovate-triangular, ca. as long as dorsal sepal near column side, ca. 9 mm wide at middle, 7-veined, midvein slightly keeled abaxially, apex acute; mentum long and narrow, straight, forming spur, slightly shorter than pedicel and ovary. Petals oblong or lanceolate, 15-20 × 4(-7) mm, 5-veined, margin irregularly denticulate, apex acute; lip subobovate or rhombic, apex nearly 3-lobed; lateral lobes subobovate, overarching column, 2 lateral lobes farther apart than width of mid-lobe; mid-lobe shallowly bilobed, margin undulate and irregularly toothed, sometimes fimbriate; disk sparsely fimbriate-lacerate along veins, central part with 3 or 4 longitudinal keeled ridges. Column ca. 5 mm, teeth triangular; anther cap nearly flatly conic, front margin densely barbate, apex subtruncate.
Epiphytic on tree trunks in mountain forests; 1200-2500 m. S Guangxi (Shangsi), SE Xizang, NW to SE Yunnan [Bhutan, NE India, Myanmar, Nepal, N Vietnam].