6. Tridynamia Gagnepain, Notul. Syst. (Paris). 14: 26. 1950.
三翅藤属 san chi teng shu
Lianas, ± tomentose-villous, glabrescent. Leaves simple, petiolate, cordate, rigidly papery or ± leathery, abaxially densely pubescent or glabrous; venation pedate. Inflorescences axillary (or terminal) bracteate racemes or panicles; bracteoles 3, sepal-like, basal to calyx. Flowers showy, fascicled. Sepals free, quincuncial, unequally enlarged, papery, with (7 or) 9 (or 11) longitudinal veins basally, veins prominent abaxially; outer 2 or 3 sepals greatly enlarged, inner ones slightly so. Corolla white or blue-violet, campanulate to broadly funnelform, 1-3.5(-5.5) cm; limb ± 5-lobed, outside pubescent apically, inside glabrous. Stamens included or exserted; filaments basally pilose or glabrous; anthers sagittate, versatile; pollen 3-colpate, not spiny. Disc 5-lobulate or absent. Pistil included or exserted; ovary unilocular; ovules 4. Style 1, threadlike; stigma 2-lobed, wrinkled. Fruit tightly enclosed in calyx, papery, indehiscent, apiculate. Seed 1, glabrous.
Four species: China, India, Laos, Malaysia, Myanmar, Thailand, Vietnam; two species in China.
Fang Rhui-cheng believes that Tridynamia is not sufficiently distinct from Porana.