Myoporum sandwicense subsp. sandwicense can grow as many-branched shrubs or small trees ranging from 1 to 10 meters tall, occasionally reaching up to 15 meters. It typically has glabrous, erect, prostrate stems. The leaves are simple and alternate, with a wide range of shapes, including elliptic, narrowly lanceolate to linear-lanceolate, or ovate, measuring 3.5–22 cm in length and 0.5–4 cm in width. The apex of the leaves is acute to long-acuminate, and the surfaces are glabrous or occasionally pubescent. These leaves are usually fleshy, sometimes chartaceous to coriaceous, and typically dry to a coriaceous texture. The margins are entire but can be serrated in young shoots or seedlings. The petioles are 0.5–2.5 cm long and usually winged, while stipules are absent. The flowers are in axillary positions, generally comprising 2–10 per cyme, with often one or more being abortive. The pedicels are terete (cylindrical) or flattened, measuring 5–17 mm long. These flowers are bisexual (perfect) and feature a calyx with (4)5(–9) lobes that are broadly ovate to lanceolate or oblong, measuring 1–5 mm long. The calyx is glandular punctate, with slightly scarious and glandular denticulate margins. The corolla is somewhat irregular, white with purplish-pink splotches, or sometimes pink, campanulate to funnelform, and 4.5–12 mm long with (4)5(–9) lobes. It is glabrous to densely pubescent within and usually glandular punctate. The nectary ring is yellow or purple at the ovary’s base. It has five stamens with anthers that open via longitudinal slits. The ovary is superior, cylindrical, narrowly conical to depressed-conical, measuring 1.5–4 mm long, and is 2-carpellate with 4–12 cells; the style is simple. The fruit is drupaceous, transitioning from greenish-white to pinkish or purplish. It is subglobose when fresh and 4–12-ribbed when dry. The bony endocarp measures 2–10 mm long and 2–9 mm in diameter. Each cell contains one spindle-shaped seed, papery when dry and 1.8–2.2 mm long. It is found in strand vegetation, dry forests, ‘a’a lava fields, mesic to wet forests, and in subalpine forests between 0-2,380 meters.