Cyanea copelandii subsp. haleakalaensis is a liana-like shrub, typically 0.3–2 meters tall, featuring tan latex. Its stems are sub-herbaceous, either reclining on moss-covered tree trunks and rooting at the nodes or growing epiphytically, with sparse branching from the base. The leaves are simple and alternate, with broadly elliptic blades measuring 10–19 cm in length and 3.5–8.5 cm in width. They have a narrowly acuminate to subcuspidate apex and a cuneate to rounded base, with glabrous upper and pubescent lower surfaces. The leaf margins are callose-denticulate, and the petioles range from 2.5 to 10 cm long. It produces inflorescences of 5–12 flowers in axillary racemes, which can appear sub-umbellate due to the sometimes unexpanded rachis. These inflorescences are pubescent with 20–45 mm peduncles and 4–16 mm pedicels. The hypanthium is obovoid, 6–10 mm long and 5–6 mm wide, and pubescent. The flowers are bisexual (perfect) with a 5-lobed calyx, yellowish corolla that appears pale rose due to dark red pubescence, 37–42 mm long and 4–5 mm wide, with a gently curved tube. The staminal column is glabrous, with anthers that are also glabrous and have apical tufts of white hairs. The ovary is inferior, 2-celled, with axile placentation, and the stigma is 2-lobed. The fruits are dark orange berries, ovoid, and 7–15 mm long, containing numerous small, smooth, shiny brown to black seeds, ca. 0.2–0.5(–2) mm long, with a straight, short to spatulate dicotyledonous embryo embedded in oily endosperm. It is found in wet forests at elevations of 1,300–1,600 meters,