Cyanea scabra is a shrub growing 0.5–1.5 meters tall, with branches that range from smooth to muricate or aculeate. The leaves are simple and alternate, with broadly elliptic to obovate blades measuring 15–23 cm in length and 7–11 cm in width. They have an acuminate apex and an obtuse base, with green upper surfaces ranging from glabrous to sparsely muricate. In contrast, the lower surfaces are pale green and may be glabrous, pubescent, muricate, or aculeate. The leaf margins are callose–dentate, and the petioles, 4–7 cm long, can be glabrous, muricate, or aculeate. Stipules are not present. The inflorescence comprises 6–12 flowers, with 15–40 mm long peduncles and pedicels 12–18 mm long. The flowers are bisexual (perfect), featuring an obconical hypanthium measuring 4–6 mm in length and 3–4 mm in width. The calyx lobes are oblong, 4–10 mm long, and 2–3 mm wide, with an apex that is obtuse, truncate, or emarginate, occasionally featuring an apiculation. The corolla is white, often adorned with pale lilac longitudinal stripes, 45–53 mm long and 5–7 mm wide, and can be either glabrous or pubescent. The tube is arcuate, and the lobes, which are often muricate, spread out to be ¼–⅓ the length of the tube. It has five stamens, which are connate and alternate with the corolla lobes, with a glabrous staminal column and anthers with apical tufts of white hairs on the lower two. The ovary is inferior and 2-celled, with axile ovule placentation. The stigma is 2-lobed and transitions from nonreceptive to receptive as the style grows through the anther tube during pollination. The fruit is a yellowish orange, ellipsoid berry, 10–13 mm long, crowned by the persistent calyx lobes, containing numerous seeds. It is found in mesic valleys in West Maui, with an elevation range of 460–850 meters.