Clermontia hawaiiensis is a species of tree or shrub that grows 1.5 to 9 meters tall and can grow in terrestrial and epiphytic conditions. The plant features repeatedly branched, spreading light gray or light brown stems with a solid pith and white, viscous latex. Its leaves are simple and alternate, with oblong or oblanceolate blades measuring 9–24 cm in length and 2.5–6.5 cm in width, possessing a dark green, glossy upper surface and a very pale green lower surface. The flowers appear in inflorescences that are usually 2 to 4-flowered and can be glabrous or pubescent. They are epigynous, zygomorphic (bilaterally symmetric), resupinate, and protandrous, with a hypanthium that is 1.7–2.2 cm long and has ten longitudinal ridges. The calyx is synsepalous with five valvate lobes that mimic the corolla’s shape, texture, and color. The perianth is tubular, greenish-white, sometimes tinged with purple or magenta, and the calyx lobes each have a prominent median longitudinal ridge. The stamens are syngenesious, with anthers that are purple or rarely greenish white and have stiff white trichomes at the apex. The ovary is inferior, consisting of two carpels and two locules, with a large axile placentation. The style is slender and surrounded by a ring of stiff white hairs near the apex, leading to a 2-lobed stigma. The fruit is an obconic, obovoid, or ellipsoid berry, measuring 2.5–3.7 cm long and 1.5–3 cm in diameter, with ten longitudinal ridges and a thick, leathery pericarp. It contains numerous tiny, dark brown or black seeds with a minutely foveate-reticulate surface and a straight, short to spatulate dicotyledonous embryo embedded in oily endosperm. It is found in montane rainforests at 550-1760 meters.