Schiedea hawaiiensis is a reclining or sprawling vine that typically grows 30 to 70 cm long in the wild, with cultivated plants potentially reaching 150 cm or more. The stems are often swollen at the nodes, terete, and conspicuously compressed-quadrangular with weakly winged angles. They are pale yellowish-green throughout or sometimes purple-tinged in the lower portion, especially in cultivation. The stems are glabrous except for sparse puberulence at the base of the internodes of the inflorescence and on the margins and adaxial surface of bracts and sepals. The leaves are simple and opposite, with ovate to elliptic-ovate blades measuring 4 to 7.8 cm long and 1.7 to 3 cm wide. The apex is acuminated to acute, and the leaf bases are often connate around the stem, ranging from acute to obtuse. The blades are thinly coriaceous, with only the midvein evident, which is slightly eccentric and purple on the lower leaves. The margins are somewhat thickened, and the petioles are 0.5 to 0.7 cm long, often flared slightly at the juncture with the stem. Stipules are absent. The flowers form in a terminal inflorescence with 12 to 50 flowers, measuring 20 to 40 cm long. Each branch, measuring 8 to 20 cm long, bears 5 to 12 flowers. The inflorescence is sparsely puberulent, with yellowish-green and foliaceous bracts. The flowers are bisexual (perfect), usually pendent, and facultatively autogamous (self-fertilizing). Sepals are 3 to 4 mm long, lanceolate, dull yellowish green to purple, concave to shallowly navicular, and puberulent. The corolla (petals) is absent. There are ten stamens with dimorphic filaments and yellow anthers. The ovary is superior, 1-celled, with free-central ovule placentation and 3 to 4 styles. The fruit is an ovoid capsule, 3.5 to 4 mm long, with 9 to 20 seeds per capsule. The seeds are 1 to 1.3 mm long, reniform-suborbicular, compressed, pale brown, with raised cells forming low transverse ridges across the surface. The perisperm (nutritive tissue surrounding the embryo) is starchy, and true endosperm is absent. It is found in a montane, dry Metrosideros polymorpha forest with Zanthoxylum hawaiiense, Dodonaea viscosa, and Tetramolopium consanguineum on a pahoehoe lava flow at an elevation of approximately 1,640 meters.