Ranunculus mauiensis is an erect to weakly ascending perennial herb, reaching heights of 50–200 cm. Its stems are sparsely to densely covered in pubescence, featuring scattered whitish hairs that range from appressed to spreading. The leaves are compound, specifically ternate, with alternately arranged cauline leaves. The leaflets are broadly ovate to deltate, with the terminal one being the largest, typically measuring 7–16 cm in length and 4–13 cm in width. The leaf surfaces are sparsely to moderately strigose, and the edges are irregularly and coarsely serrated and lobed, while the margins of the cauline leaves can be entire or serrate. The leaves are petiolate, and stipules are absent. The flowers are dichotomously branched in loose cymes. These flowers are bisexual (perfect) and actinomorphic (radially symmetric), with a calyx comprising five sepals lanceolate to ovate, approximately 4–5 mm long, and reflexed. The corolla consists of five obovate, yellow, glossy petals, each 3.5–4.5 mm long. The stamens are numerous, with dithecal anthers that open via a longitudinal slit. The superior ovary has numerous one-celled carpels. The fruit consists of multiple achenes forming a globose head; each achene is obovate-suborbicular, about 2–2.2 mm long, glabrous, slightly margined, with smooth or minutely pitted faces, and a straight or somewhat curved beak measuring 0.6–0.9 mm long. The seeds contain an abundant endosperm and a small embryo. It occurs in open sites within mesic to wet forests and along streams between 1,060-1,710 meters.