Liana; sap milky, copious; stems glabrous, hollow and lenticellate in age, with a prominent interpetiolar ridge. Leaves opposite, glabrous; stipules 2, broadly ovate, softly puberulent, 2-3 mm long; petioles 1-2 cm long, stout; blades +/- elliptic to ovate, shortly and bluntly acuminate, obtuse to subcordate at base on larger leaves, 12-24 cm long, 6-12.5 cm wide, bicolorous, the midrib above pale green, impressed, lacking a central rib; reticulate veins prominulous and very closely spaced below. Thyrses axillary or terminal; axes of inflorescences, pedicels, and calyces densely puberulent; pedicels to 3 cm long; flowers 5-parted; calyx lobes narrowly ovate, 4-9 mm long, each with several squamellae inside; corolla tubular, 5-6.5 cm long, the tube pale green, minutely puberulent, constricted ca 1 cm above base, the lobes white, spreading at anthesis, ca 1 cm long but with one side extended laterally 2-2.5 cm; stamens included, attached at base of corolla throat, ca 2 cm long; filaments and anthers pubescent; anthers 5-6 mm long, connate, glued to the fusiform stigma; stigma 1; nectaries growing together, covering ovary. Follicles paired, widely divergent, cylindrical, 11-16 cm long, 1.5-2 cm diam, densely pubescent with short erect trichomes; pericarp with a thin leathery outer layer and a thicker woody layer; seeds many, the seminiferous portion cylindrical to angulate or flattened, 13-20 mm long, obscurely striate, brown, narrowed only a few millimeters at apex; plume at apex light brown, to 6 cm long. Croat 8633, Knight 6988. Occasional, in the forest, probably less common than O. macrantha. Individuals flower intermittently throughout the dry season. Some fruits have been seen dispersing seeds in August. Because flowers are a pale greenish color, with a very long corolla tube, and fall profusely in the early morning, I suspect that the plant is pollinated by hawkmoths.