Schiedea haakoaensis is an erect, strongly ascending subshrub typically reaching 70 to 100 cm. The plant usually has a single stem, sometimes with a few short side branches, and is noticeably quadrangular in shape. The stems are pale green, with distal internodes often having a purple tinge, and are glabrous except on the internodes of the inflorescence, bracts, and sepals. The leaves are opposite, with blades measuring 3 to 18 cm long and 1.2 to 4.5 cm wide. The leaf shape varies from narrowly to broadly elliptic, sometimes lanceolate to oblanceolate, with an acute to acuminate apex. The leaves are pale to yellowish green, occasionally with younger ones being purple-tinged, slightly thickened, rubbery, and chartaceous when dry. The midvein is somewhat eccentric and is the only evident vein. The petioles are 0.5 to 1 cm long and weakly grooved. The inflorescence is terminal, measuring 40 to 50 cm long, with up to 80 or more flowers. It is diffuse and erect, with lateral branches 11 to 18 cm long and ascending. Each branch bears 6 to 20 flowers, with tertiary and higher-level internodes usually ascending or appressed. The pedicels typically spread at anthesis, sometimes with a few minute curved hairs along the inflorescence internodes. The bracts are generally yellowish green and foliaceous, with those in the upper part of the inflorescence subtending the flowers being subulate, purple, and usually yellowish green near the base. The pedicels are 4 to 6 mm long at anthesis and elongate slightly in fruit. The sepals are 3 to 4.1 mm long, lanceolate, purple, and sometimes greenish toward the base. The nectary shaft is 1.5 to 2.1 mm long, gently recurved, with a weakly bifid apex. Ten stamens with weakly dimorphic filaments and yellow anthers dehisce after the flower opens. The styles number 3 has elongated stigmas that are receptive when the flower opens. The fruit is an ovoid capsule, 4.3 to 5 mm long, containing approximately 1.0 mm long seeds, suborbicular, slightly asymmetrical, compressed, brown, and with a rugose surface. It was found in mesic forest environments around 1,525 meters.