Description from Flora of China
Callista densiflora (Wallich) Kuntze; Dendrobium clavatum Roxburgh (1832), not Wallich ex Lindley (1852).
Stems strongly clavate, swollen, ± pseudobulbous at base, 25-40 cm, to 2 cm in diam., internodes clavate, expanding to a swollen node, obscurely 4-angled, sometimes ridges inconspicuous, yellow, pale brown and glossy when dry, sheathless. Leaves 3 or 4, subterminal, oblong-lanceolate, 8-17 × 2.6-6 cm, leathery, base not decurrent into clasping sheath, apex acute. Inflorescence subterminal, pendulous, densely many flowered; peduncle with 2-4 sheaths at base; rachis 6-16 cm; floral bracts broadly oblong or obovate, 12-15 × 6-10(or more) mm, membranous, strongly ca. 10-veined, revolute, obtuse. Pedicel and ovary whitish green, 2-2.5 cm. Flowers spreading, 3-4 cm in diam.; sepals and petals pale yellow, lip golden yellow, column and anther cap orange-yellow. Dorsal sepal ovate, 17-21 × 8-12(or more) mm, 5-veined, obtuse; lateral sepals nearly as large as dorsal sepal, ovate-lanceolate, 5- or 6-veined, apex subacute; mentum subglobose, ca. 5 mm wide. Petals suborbicular, 15-20 × 11-15 mm, with 3 main veins and many secondary veins, base contracted into a short claw, margin erose above middle; lip orbicular-rhombic, 17-22 × up to 22 mm, both surfaces densely lanate above middle, shortly clawed, both sides embracing column below middle, apex rounded. Column ca. 4 mm; anther cap compressed subglobose or conic, front margin truncate, finely notched.
S. Y. Hu (Quart. J. Taiwan Mus. 26: 151. 1973) misidentified material of this species as Dendrobium amabile (Loureiro) O’Brien.
Seidenfaden (Opera Bot. 83: 23. 1985) included Dendrobium guibertii Carrière (Rev. Hort. 48: 431. 1876), from N Thailand, in the synonymy of D. densiflorum. However, H. P. Wood (Dendrobiums, 637-638. 2006) maintained it as a distinct, late-flowering (July-August) species, conceding that its true distribution remains unclear because of prevalent misidentification. A brief description is provided here for comparison with D. densiflorum. Stem clavate, to 80 cm, 4-grooved. Leaves 3-5, usually 4, ca. 10.5 × 5.5 cm. Inflorescence pendulous, 22-30 cm, developing very rapidly, with buds packed together, as in D. densiflorum, up to 60-flowered. Flowers ca. 4 cm in diam., sepals and petals pale yellow, lip deeper yellow.
Epiphytic on tree trunks in evergreen broad-leaved forests, lithophytic on rocks in mountain valleys; 400-1000 m. N Guangdong, Guangxi, Hainan, SE Xizang [Bhutan, NE India, Myanmar, Nepal, N Thailand].