Achyranthes sandwicensis is a shrub or small tree, which can be branched from the base or sometimes have a single trunk with a branched crown, reaching heights of 0.8 to 4 meters and occasionally up to 7 meters. The stems, 2 to 10 cm in diameter, are covered with silky canescent straight, appressed hairs. Its leaves are simple and opposite, typically elliptic to ovate, with dimensions ranging from 1.5 to 13 cm in length and 1 to 7.6 cm in width. The leaves have various apex forms, including acuminate, acute, obtuse, or sometimes retuse, with a base from cuneate to truncate. The leaf surfaces are usually densely pubescent, particularly on the lower side, with entire margins with pinnate venation. The petioles are 3 to 20 mm long. It features stout spikes of flowers measuring 0.5 to 3 cm in length and 5 to 10 mm in diameter, with peduncles ranging from 0.5 to 7.5 cm long. The flowers are bisexual, lanceoloid to narrowly ovoid, and actinomorphic (radially symmetric), subtended by a persistent bract and two bracteoles. The calyx has four sepals, each 2 to 4 mm long, which can be pubescent or rarely glabrous. It does not have petals and possesses four stamens that are connate at the base and a superior ovary that is 2 to 3(4)-carpellate. The fruit is an utricle, about 2 mm long, enclosed by the calyx, containing a single seed. The surface of the seed is usually lustrous, and the seed lacks an endosperm. It is found in open dry forests, on exposed ridges, and lava fields between 0-750 meters.