Descripción: Plantas trepadoras o lianas con tronco cilíndrico y cubierto de lenticelas granulares. Ramitas con surcos longitudinales y lenticelas blancas. Hojas bifolioladas y opuestas, a veces con un zarcillo simple. Folíolos de 4-14 x 2-10 cm, ovados, con ápice acuminado a obtuso, bordes enteros y base redondeada o decurrente. Las hojas tienen pelos amarillentos por el envés, principalmente sobre las nervaduras. Pseudo-estípulas deciduas. Flores con cáliz pateliforme, corola lila o morada, estambres didínamos. Frutos en cápsulas, de 10-39 x 1-1.5 cm. Semillas aladas.

Especies Parecidas: A menudo se confunde con LK arrave Arrabidaea verrucosa LK2 , pero en A. verrucosa la corteza exterior del tronco es exfoliante en láminas delgadas y los frutos son tuberculados en la superficie exterior. También se puede confundir con LK arraca Arrabidaea candicans LK2 , pero en A. candicans los folíolos tienen el envés blanco.

Liana; trunk light brown; outer bark soft with large corky lenticels; stems terete, lenticellate, with an interpetiolar ridge, glabrate in age; tendrils simple; pseudostipules foliaceous, to 1 cm long, falcate, caducous. Leaves bifoliolate or rarely simple; petioles 1.1-3.5 cm long; petiolules 0.5-2.2 cm long; petioles and petiolules short-pilose; leaflets ovate to obovate, obtuse to caudate-acuminate, obtuse to rounded or subcordate at base, 5-15 cm long, 3-10 cm wide, lepidote on both surfaces, otherwise glabrous above, villous at least on veins below, usually with tufts or cavelike domatia in axils below, entire or rarely dentate on juveniles. Inflorescences large, pyramidal, axillary or terminal panicles; flowers red-violet to violet-purple, whitish-tipped in bud; branches and pedicels lepidote and white-villous; calyx bowl-shaped, 1-4 mm long, 4-8 mm wide, flared, the margin entire, wavy; corolla 2.5-4.7 cm long, the tube glabrous except for gland-tipped trichomes at point of staminal attachment inside, the lobes sparsely pubescent on both sides; stamens included, with the longer ones 1.1-1.3 cm long, the shorter ones 0.8-1 cm long, the thecae divaricate, to 2 mm long; staminodium 3-4 mm long, held on 2-lobed side of corolla opposite nectar guide, this side whitish and spotted inside; pistil 1.5-2.3 cm long; ovary linear, 1.5-2.5 mm long, slightly lepidote. Capsules linear, flattened, 15-39 cm long, 1.1-1.5 cm wide, with medial rib faint or prominent, densely lepidote, often sparsely whitish-lenticellate; seeds ca 1 cm long and 2.5-4 cm wide, the outer margin rounded to truncate, the lateral margin of wings translucent. Croat 6052, 13161. Common along the shore and occasional in the forest. Flowers most abundantly from July to September (sometimes from June to November), rarely in January and February; the flowers are abundant on an individual vine for over a month, but each flower lasts only one day. The fruits mature mainly in the middle of the dry season. The species can be recognized by its open, bowl-shaped calyces and white-tipped buds. Vegetative characteristics include the dense pubescence on the main veins beneath, the pubescent petioles and petiolules, and the frequency of simple leaves. Petastoma breviflorum Standl., reported by Standley as a distinct species on the basis of its shorter corolla, appears to be inseparable from this species. Corolla length in the family is variable. Southern Mexico to Amazonian Brazil. In Panama, known on the Pacific slope, most commonly from premontane moist forest in the Canal Zone and Panama; known also from tropical moist forest in the Canal Zone, Veraguas, Herrera, Panama, and Darien, from tropical dry forest in Herrera, from premontane wet forest in Chiriqui, Panama, and Darien, and from tropical wet forest in Panama.