Bobea sandwicensis is a tree that can reach up to 10 meters in height. The young branches of these trees are approximately 2 mm in diameter toward the apex and are covered with a sericeous-puberulent texture. The simple, opposite leaves are ovate to lanceolate or elliptic, measuring between 3 and 11.5 cm in length and 1.5 to 7 cm in width, with an acute to acuminate apex and an obtuse to rounded, subcordate, or rarely acute base. The leaf surfaces are generally glabrous, with the lower surfaces sparsely pubescent along the midrib and secondary nerves. Chartaceous to subcoriaceous in texture, the leaves have entire margins with secondary veins that are often reddish and pellucid. The petioles are 5 to 15 mm long, while the stipules are deltate to lanceolate, 3 to 5 mm long and 2 to 4 mm wide, with a villous upper surface and an appressed sericeous lower surface. The flowers, which can be either staminate (male) and perfect (bisexual) or functionally unisexual, are organized in cymes of 3 to 7 flowers, with peduncles measuring 6 to 25 mm in length for staminate and perfect flowers, and 8 to 20(-35) mm for pistillate (female) flowers. They are 4(5)-merous, often heterostylous, with a persistent calyx limb in fruit. The calyx limb is cupular and broadly lobed, while the corolla ranges from greenish to yellowish or sometimes white. The staminate and perfect flowers have a salverform corolla with a 5 to 11 mm long tube and lobes approximately 3 mm in size. In contrast, pistillate flowers have a similar corolla form but with a slightly shorter tube. The fruit is drupaceous, purplish to black, subglobose, and measures 6 to 10 mm in diameter, with sparsely pubescent pyrenes (2–)5–6 that are thick-walled and 1-seeded. The seeds lack and endosperm. It is primarily found in dry to mesic forests and on open, sparsely vegetated lava flows at 100-1220 meters