Melicope peduncularis is an erect or sprawling shrub, sometimes developing into shrubby trees reaching 1–4 meters in height. The new growth is finely scurfy and sparsely to densely grayish puberulent, becoming glabrate over time. The leaves are simple and can be opposite or, on O‘ahu, arranged in whorls of 3–4 per node. The blades are narrow to broadly elliptic or suborbicular, with a rounded and usually emarginate apex and a broadly cuneate, rounded, or cordate base. They are glabrous or sparsely puberulent along the midrib, with a strong anise odor when crushed. The upper surfaces are darker green, coriaceous, and measure 3–23 cm long and 2–12 cm wide. Margins are often revolute near the base and are entire. The midrib is usually tinged red or purple, with 8–12 pairs of primary lateral veins connected by an arched submarginal vein and higher-order venation forming a reticulate pattern. The petioles are 13–50 mm long, glabrate or sometimes puberulent, and absent stipules. The flowers are arranged in minutely grayish puberulent to glabrate cymes of 3–21 flowers, with stout peduncles 7–40 mm long and stout pedicels 3–6 mm long. Bracteoles are lanceolate, with the upper ones deltate, 1–3 mm long, minutely ciliate, and sparsely puberulent. Bracts are small and opposite. The flowers can be bisexual (perfect) or functionally unisexual, with plants being monoecious. The calyx has four sepals, which are deltate-ovate and about 2 mm long, sparsely puberulent in both staminate and pistillate flowers. The corolla consists of 4 narrowly ovate petals, which are glabrous, with staminate flowers having petals 7–8 mm long and pistillate flowers having petals 5–6 mm long. There are eight stamens in 2 whorls, distinct and reduced but always present in functionally pistillate flowers, with a glabrous nectary disk. The pistillate flowers have a superior ovary that is 4-celled and 4-lobed, glabrous, with connate carpels and two hemitropous ovules per cell. The style is reddish, filiform, about 2 mm long, terminating in 4 short stigmatic branches. Staminate flowers have a rudimentary ovary. The fruit is a dark green capsule, 6–14 mm long and 13–28 mm wide, with carpels completely connate or connate up to about two-thirds of their length. The exocarp is glabrous and glandular punctate, with the carpels dehiscing along the upper suture. The seeds are usually 2 per carpel, 3–4 mm long, glossy black when ripe, crustaceous, ovoid, sometimes angled from compression, with a straight embryo in fleshy endosperm, short radicle, compressed ovate cotyledons, and a brown warty putamen. It is found in mesic forests between 300-1,160 meters.