5. Marsdenia tenacissima (Roxburgh) Moon, Cat. Pl. Ceylon. 21. 1824.
通光散 tong guang teng
Asclepias tenacissima Roxburgh, Pl. Coromandel 3: 35. 1819; Gymnema tenacissima (Roxburgh) Sprengel.
Lianas robust, densely pilose to tomentose throughout except for interior of corolla. Petiole 5-6 cm, slender; leaf blade ovate, 8-10 × 6-6.5 cm, base deeply cordate with rounded sinus, apex acuminate; basal veins 5-7, lateral veins 2 or 3 pairs. Inflorescences much branched, broader than long, to 8 × 12 cm, many flowered; peduncle to 2 cm, shorter than first internode. Pedicel 6-8 mm. Sepals elliptic-lanceolate, ca. 3 × 1-1.3 mm, tip rounded. Corolla "yellow," campanulate, with spreading lobes, very densely pilose outside; tube ca. 3.5 × 2.5 mm, interior retrorsely pilose toward base; lobes oblong, ca. 4 × 2.2 mm, apex rounded, minutely velvety. Corona lobes exserted from corolla tube, oblong, apex truncate-emarginate with corners produced into short horns, sometimes toothed between these. Anther appendages oblong, slightly longer than corona lobes; pollinia curved cylindric. Stigma head broadly cylindric, concealed by anther appendages.
Cliffs; ca. 1500 m. Yunnan (Szemoo) [Cambodia, India, Laos, Myanmar, Nepal, Sri Lanka, Thailand, Vietnam]
The stems yield very strong fibers, reputedly among the strongest produced by any plant, that are used for making cords and strings.