Ranunculus hawaiensis is an erect or ascending perennial herb with fibrous roots ranging from 50 to 200 cm tall. The stems are densely covered with hispid hairs that are golden or whitish, and these hairs can be spreading to erect. The basal leaves of this plant are twice ternately compound, with lanceolate to ovate leaflets measuring typically 5 to 7 cm in length and 4 to 7 cm in width, where the terminal leaflet is the largest. These leaflets are irregularly toothed and lobed, with the teeth being usually bluntly acute to obtuse and the surfaces moderately to densely strigose. The flowers are in branched, relatively open cymes. The receptacle of the flower is conical and hirsute. The sepals are five in number, yellowish-green, lanceolate to ovate, and approximately 5.5 to 8 mm long, tending to be reflexed. The petals, numbering five to ten, are yellow with a glossy upper surface, obovate, and about 7 to 10 mm long, each featuring a scale-covered nectary at the base. These flowers are bisexual (perfect) and actinomorphic (radially symmetric). The fruit consists of numerous achenes forming an ovoid head. Each achene is obovate-suborbicular, roughly 5 mm long, and edged with a narrow wing. The surfaces of these achenes are minutely but conspicuously pitted, with a straight or slightly curved beak measuring between 0.9 and 1.2 mm in length. The seeds have a copious endosperm with a small embryo. It occurs in mesic forests, grassy slopes and scree, and open pastures between 1,800-2,000 meters.