Description from Flora of China
Callista annamensis Kraenzlin; C. hercoglossa (H. G. Reichenbach) Kuntze; C. vexans (Dammer) Kraenzlin; Dendrobium hercoglossum var. album S. J. Cheng & C. Z. Tang; D. poilanei Guillaumin; D. vexans Dammer; D. wangii C. L. Tso.
Stems pendulous, pale yellow when dry, cylindric or sometimes thickened from base to upper part, usually 8-40 cm, 2-5 mm in diam., with few to many nodes, internodes 1.5-2 cm. Leaves narrowly oblong or oblong-lanceolate, 4-10 × 0.4-0.8(-1.4) cm, leathery, with tightly clasping sheaths at base, apex obtuse and unequally bilobed. Inflorescences often several, arising from old leafless stems, 2- or 3-flowered; peduncle green, 6-10 mm; rachis sometimes slightly upcurved, 1.5-2 cm, thin and weak, base with 3 or 4 short tubular sheaths; floral bracts ovate-lanceolate, small, 3-5 mm, dry membranous, apex acute. Pedicel and ovary pale pinkish red, 1.2-1.5 cm. Flowers spreading; sepals and petals pale pink, lip white, epichile pale pink, column white, anther cap purple. Dorsal sepal ovate-oblong, 13-18 × 5-8(or more) mm, 7-veined, apex acute; lateral sepals slightly obliquely ovate-lanceolate, ca. as large as dorsal sepal, 7-veined, apex acuminate; mentum very short. Petals obovate-oblong, 12-15 × 4.5-7(or more) mm, 3-veined, apex acute; lip erect, ca. 1 cm, with epichile and hypochile; hypochile subglobose, inner surface densely barbellate, apex densely shortly fimbriate; epichile deltoid, relatively small, glabrous, apex acute. Column ca. 4 mm, lower part enlarged, foot ca. 2 mm, column teeth deltoid, apex slightly obtuse; anther cap subspherical, densely finely papillate, front margin erose.
Epiphytic on tree trunks in dense mountain forests, lithophytic on damp rocks in valleys; 600-1300 m. SW Anhui (Huo Shan), SW Guangdong (Xinyi), Guangxi, SW Guizhou, Hainan, Hunan (Jianghua), S Jiangxi, SE Yunnan [Laos, Malaysia, Thailand, Vietnam].