Cyanea membranacea is a sparingly branched shrub reaching 2–4 meters tall. Its leaves are alternate and simple, oblanceolate to oblong blades measuring 18–32 cm in length and 3–9 cm in width. The leaves have obtuse to acute apices and cuneate bases, with the upper surfaces being green and either glabrous or sparsely pubescent and the lower surfaces pale green and pubescent. The leaf margins are callose–serrated, and the petioles are 4–12 cm long. The axillary inflorescence comprises 7–12–flowers with purple, broadly obovoid hypanthia and dentiform calyx lobes. The zygomorphic (bilaterally symmetric) corolla is white to pale purplish, 30–40 mm long and 3–4 mm wide, and can be sparsely pubescent or nearly glabrous. The stamens, five in number, are connate with a glabrous staminal column and glabrous anthers, the lower two of which have apical tufts of white hairs. The fruits are purple, globose berries that are 8–10 mm long, with numerous small seeds that are brown to black, smooth, and shiny that are ca. 0.5–0.6 mm long, with a straight, short to spatulate dicotyledonous embryo embedded in oily endosperm. It is found on shaded slopes and gulches within mesic forests at 580-730 meters.