Description from Flora of China
Callista williamsonii (J. Day & H. G. Reichenbach) Kuntze.
Stems cylindric, sometimes swollen and fusiform, to 20 cm, 4-6 mm in diam., unbranched, with several nodes, internodes 2-3 cm, golden yellow when dry. Leaves several, usually alternate on upper part of stem, oblong, 7-9.5 × 1-2 cm, leathery, with dense black rigid hairs especially on sheaths, base decurrent forming clasping sheaths, apex obtuse and unequally bilobed. Inflorescences subterminal, 1- or 2-flowered; peduncle 5-10 mm; basal sheaths 3 or 4, short; floral bracts ovate, ca. 5 mm, papery, acute; ovary not carinate. Flowers spreading; sepals and petals pale yellow or white, lip pale yellow or white, disk tinged with tangerine. Dorsal sepal narrowly ovate-oblong, 25-34 × 6-9(or more) mm, narrowly keeled abaxially, 5-veined, acuminate; lateral sepals similar to dorsal sepal but oblique at base, 5-veined; mentum rigid, straight, 15-20 mm, forming spur. Petals similar to sepals; lip ca. 2.5 cm, 3-lobed; lateral lobes embracing column, subobovate, front margin slightly undulate; mid-lobe suborbicular or broadly elliptic, margin undulate, apex acute; disk sparsely shortly fimbriate along veins. Column ca. 6 mm; anther cap broadly conic, front margin densely shortly barbate.
Epiphytic on tree trunks in forests; ca. 1000 m. N Guangxi, Hainan (Wuzhi Shan), SE and W Yunnan [NE India, Myanmar, Vietnam].