Cyanea angustifolia is a shrub growing 1.5–5 meters tall, featuring white, yellow, or tan latex, with unarmed, muricate, or aculeate branches. The leaves are simple and alternate, with lanceolate, narrowly elliptic, or narrowly oblong blades measuring 9–32 cm long and 1.5–5.5 cm wide. The apex is acuminate, and the base ranges from cuneate to attenuate. The upper surfaces of the leaves are green and glabrous, while the lower surfaces are pale green, either glabrous or pubescent along the midrib. The margins are callose-crenulate to callose-crenate. The inflorescences comprise 6–25 flowers in axillary racemes that are spreading or pendent. The peduncles are 15–240 mm long, and pedicels range from 8–30 mm long. The flowers are bisexual (perfect), with a purple, obovoid hypanthium and a 5-lobed calyx with dentiform lobes. The corolla is white to greenish white, sometimes tinged pale purplish, 20–30 mm long, and glabrous. The stamens are five in number, with glabrous anthers and apical white hair tufts. It produces purple, globose berries that are 5–10 mm long, containing numerous small, brown to black, smooth, and shiny seeds, ca. 0.6-0.8 mm long, with a straight, short to spatulate dicotyledonous embryo embedded in oily endosperm. It is found in mesic to wet forests and valleys between 150–760 meters.