Cyanea acuminata is a shrub standing 0.3–2 meters tall and features white, yellow, or tan latex with sub-herbaceous stems that are woody only at the base, unbranched, or sparingly branched. It can be unarmed, muricate, or aculeate. The leaves are simple and alternate, with oblanceolate to narrowly obovate or elliptic blades measuring 11–32 cm in length and 3–9 cm in width. The apex is narrowly acuminate, and the base ranges from attenuate to cuneate. The leaf surfaces are green, glabrous, or sparsely pubescent on top, whitish-green, and pubescent at least on the midrib and veins beneath, with minutely callose-denticulate margins. The inflorescences are axillary racemes with 6–20 flowers, pubescent, and the peduncles are 15–60 mm long. The calyx is 5-lobed with narrowly triangular lobes, and the corolla is zygomorphic, glabrous or pubescent, white, sometimes tinged purplish, 30–35 mm long, with the lobes spreading and ¼–⅓ as long as the tube—the five stamens, with pubescent or rarely glabrous anthers and apical white hairs. The fruit is a yellow to yellowish orange berry, globose, and 4–6 mm long, containing numerous small, brown to black seeds that are smooth, shiny, and a straight, short to spatulate dicotyledonous embryo embedded in oily endosperm, approximately 0.2-0.5(-2) mm long. It is found in mesic valleys at elevations of 300–730 meters.