Cyanea coriacea is a branched or unbranched shrub ranging from 2.5 to 4 meters in height. The leaves are simple and alternate, with oblong to oblanceolate blades measuring 17-38 cm in length and 4-12 cm in width. The leaf apex is rounded, and the base is cuneate. The upper surfaces of the leaves are green and glabrous, while the lower surfaces are pale green and either glabrous or very sparsely pubescent along the midrib. The leaf margins are minutely callose–crenulate. Petioles range from 5 to 16 cm in length, and stipules are absent. The flowers are borne in inflorescences of 12 to 20 flowers, with a condensed or obsolete rachis. Peduncles measure 25 to 80 mm long, and pedicels range from 12 to 18 mm long. Each flower is bisexual (perfect) with an obovoid hypanthium measuring 4 to 5 mm long and 3 to 4 mm wide. The calyx lobes are dentiform, 0.5 to 1 mm long, with pubescent margins and an acute to acuminate apex. The corolla is white, often striped or tinged with purple, 20 to 30 mm long and 2 to 3 mm wide, glabrous, with a suberect tube and spreading lobes. There are five stamens, alternate with the corolla lobes and fully connate into a staminal column that is glabrous. The anthers are also glabrous, with the lower two bearing apical tufts of white hairs. The ovary is inferior and 2-celled, with axile placentation. The stigma is 2-lobed and either wet or dry, remaining appressed and nonreceptive while the style grows through the anther tube to release pollen. Once pollination occurs, the stigma lobes spread apart and become receptive. The fruit is a globose, purple berry measuring 6 to 10 mm in length and contains numerous seeds. It occurs in mesic valleys of northern Kauaʻi between 150-220 meters.