Bidens mauiensis is a decumbent perennial herb typically growing between 10 and 30 cm tall. The leaves are highly variable, ranging from simple to bipinnately compound, and are divided into narrow ultimate segments. They are generally 4–7.5 cm long, including the petiole. Leaflets number from 1 to 7 (most often 3 to 5) and are lanceolate, rhombic, or linear in shape, measuring 0.5–5 cm in length and 0.2–2.5 cm in width. The leaf surfaces are glabrous or sparsely pubescent along the veins, and the margins are serrate. The flowering heads are solitary, terminating the main stem and lateral branches. They measure 2.8–5.3 cm in diameter when including the ray florets, though the heads may become noticeably smaller late in the flowering season or on older plants. Peduncles are 10–25 cm long and sparsely pubescent. The involucre has outer and inner bracts, with the outer ones measuring 5–15 mm long. Each head has (5–)7–11 ray florets, which are sterile and yellow, with rays 15–28 mm long and 7–8 mm wide. The disk florets, 18–42 per head, are perfect with yellow corollas. The pappus consists of wide awns decurrent into the wings and measures 0.5–1.5 mm long, though it is sometimes absent. The fruit is a brown achene that is straight, winged, and glabrous, measuring 4.5–10 mm long and (1.5–)2–3.8 mm wide. It is found in dry coastal habitats and occasionally in shrublands on dry slopes between 50-600 meters.