Liana; branchlets, petioles, and rachises angled, hexagonal, lepidote, pubescent with stellate and simple trichomes; stems with conspicuous interpetiolar ridges; tendrils trifid; pseudostipules sickle-shaped, to 5 mm long, densely lepidote and stellate-pubescent, caducous. Leaves 2- or 3-foliolate; petioles 2.3-7 cm long; petiolules 0.6-4.3 cm long; leaflets broadly ovate to rounded, acuminate, cordate at base, 2.5-16 cm long, 2-10.7 cm wide, sparsely glandular-lepidote on both surfaces, the upper surface glabrous except on veins, the lower surface tomentulose with dense, short, stellate trichomes and with longer, usually branched trichomes dense on veins and very sparse elsewhere (younger leaves puberulent above). Panicles +/- racemose, terminal; flowers 5-parted, aromatic, white, usually variously tinged with maroon, turning deep purple, 3-4 cm long; calyx enveloping one-third of corolla, the margin broad, double, +/- lobed and undulate; corolla 3-4 cm long, fleshy, bilabiate, with 3 narrow lobes opposing a single broad lobe; stamens included, the longer pair to 1.8 cm long, the shorter pair to 1.5 cm long, the thecae divaricate, ca 2 mm long; staminodium 3-5 mm long, inserted 4-5 mm from base of corolla; ovary densely tomentulose. Capsules oblong-ellipsoid, blunt to subcordate on either end, 9-16 cm long, to 4.5 cm wide; valves broadly ridged along middle, with an obscure medial groove or ridge, densely glandular-puberulent; seeds chiefly to l.5 (2) cm long and (2.7-3) 6.5 cm wide, the wings narrower toward the deeply lacerate lateral margins. Croat 12499, Foster 1918. Recognized by the unusual double calyx and the hexagonal stems with stellate trichomes. Mexico to Argentina; West Indies. In Panama, widespread and ecologically variable; known from tropical dry forest in the Canal Zone, Los Santos, Herrera, and Panama, from tropical moist forest all along the Atlantic slope and on the Pacific slope in the Canal Zone, Veraguas, Herrera, Panama, and Darien, from premontane wet forest in Colón, Chiriqui, Veraguas, Coclé, and Panama, from premontane rain forest in Darien, and from lower montane wet forest in Chiriqui.