Zanthoxylum hawaiiense, a member of the rue family (Rutaceae), is a medium size, long-lived perennial tree 3 to 8 m (10 to 26 ft) tall, with a trunk 25 cm (10 in) in diameter. The bark is pale to dark gray, and the leaves are lemon-scented. Alternate leaves are composed of three leaflets, one being terminal and two lateral. The terminal leaflet is subtended by a 2-jointed leafstalk, 1.5 to 5.2 cm (0.6 to 2.0 in) long, while the lateral stalks are 1-jointed, 1 to 4 cm (0.4 to 1.6 in) long. Triangular-oval to lance-shaped, toothed leaflets, 3.4 to 10.0 cm (1.3 to 3.9 in) long and 1.5 to 5.0 cm (0.6 to 2.0 in) wide and are thin or sometimes thick in texture. The surfaces are usually without hairs, or the lower may be finely hairy and glandular. Fifteen to 20 flowers are arranged in open flower clusters, 4.0 to 8.0 cm (1.6 to 3.1 in) long, which are subtended by main flower stalks 2 to 5 cm (0.8 to 2.0 in) long. Each flower is subtended by a flower stalk, 2.0 to 4.0 mm (0.08 to 0.2 in). Usually, all flowers on a tree are of one sex, either male or female. Four narrowly triangular, sparsely hairy sepals are 1.0 mm (0.04 in) long. Four green-white oblong to lance shaped petals, 3 to 6 mm (0.1 to 0.2 in) long, sometimes are absent in male flowers. A sickle-shaped, round-tipped fruit, 8 to 10 mm (0.3 to 0.4 in) long, opens on one side to release one round, slightly compressed seed. The seed covering is pitted and sculptured, about 7 to 8 mm (0.27 to 0.31 in) long.