Cyanea pinnatifida is a shrub reaching 0.8–3 meters tall, with either unbranched or sparingly branched stems, and exhibits glabrous or sparsely muricate textures. The leaves are simple and alternate, featuring pinnately parted blades 25–60 cm long and 3.5–8 cm wide (between the segments), expanding to 8–25 cm wide across the segments. Each leaf typically has 2–6 segments per side, which are narrowly oblong and 1–2.5 cm wide. The leaf apex is either acute or obtuse, with glabrous upper surfaces and lower sparsely pubescent. The leaf margins are minutely callose–denticulate, and the petioles are 3–7 cm long. It bears 8–15–flowered inflorescences, which are pubescent, with peduncles 40–50 mm long and pedicels 10–15 mm long. The bisexual (perfect) flowers feature an obconical, pubescent hypanthium measuring 10–12 mm in length and 6–8 mm in width. The calyx lobes are triangular, 3–5 mm long, and 2–2.5 mm wide, with an obtuse apex. The corolla is greenish-white with purplish longitudinal stripes at the base, 36–50 mm long and 4–5 mm wide, and sparsely pubescent. The corolla tube is suberect to slightly curved, with spreading lobes. Five stamens alternating with the corolla lobes, connate, with a white, sparsely pubescent at the base staminal column and glabrous anthers; the lower two have apical tufts of white hairs. It grows in diverse mesic forests within the central Wai’anae Mountains of O’ahu.