Annual or perennial climber; stem very long, about 2-5 m, slender, purplish, glabrous or slightly villous; leaves alternate, thin, acute to acuminate, ovate to cordate with rounded base; petioles 3-7 cm long; peduncles 1-3 flowered, as long as the petioles, glabrous or pilose; sepals ovate, acute, nearly glabrous, reflexed; corolla campanulate, 2-3 cm across, yellow with dark purple throat, tube narrow, mouth wide, glabrous; stamens 5, usually included, anthers never twisted, filament filiform or dilated below, often unequal; ovary 2 locular, style slender, stigma globose or capitates; capsules 2-valved, ovoid, subacute, glabrous; seeds 4 or 2, ovoid, dark brown, covered with soft, brown, velvety pubescence.