Sanicula purpurea is a perennial herb, stout and either erect or ascending, standing 8 to 36 cm tall, emerging from a massive, multicipital caudex. It has several decumbent, tufted stems that branch paniculately-cymosely. The leaves are simple and alternate, with numerous basal and progressively reduced cauline leaves up the stem. Basal leaves are reniform, orbicular, or ovate-cordate, measuring 2 to 8 cm wide, and are 3-7-lobed halfway to the petiole, with orbicular to obovate lobes. These leaves are coriaceous with crenate-serrate margins featuring mucronate teeth. Cauline leaves are palmately 3-5-cleft to below the middle with obovate lobes, transitioning from petiolate to subsessile along the stem. Basal petioles are slender, ranging from 5 to 25 cm long, and abruptly sheathing at the base, with no stipules. The flowers are arranged in paniculate, terminal clusters forming 1-3 pedunculate, capitate umbels, supplemented by similar clusters in the upper leaf axils, each 6-10-flowered. Peduncles are 0.5 to 1.5 cm long with an involucre of about ten oblong or oblanceolate bracts, 3-6 mm long. It bears 1-3 perfect flowers sessile and 5-7 staminate flowers on roughly 3 mm long pedicels. The calyx teeth are ovate, 1-1.5 mm long, obtuse, nearly distinct, and extend beyond the fruit prickles in fruit. The corolla consists of five purple or cream-colored petals tinged with purple. The plant has five stamens attached to an epigynous disk, with an inferior, 2-celled ovary containing one ovule per cell. The styles, swollen at the base into a stylopodium, recurved slightly longer than the calyx teeth. The fruit is subglobose, 2-3.5 mm long, and 2-3 mm in diameter, with mericarps somewhat dorsally compressed, covered with slender, straight or slightly curved, bulbous-based prickles, and inconspicuous vittae. Each mericarp houses one seed with a lanceolate commissural scar on a shallowly concave commissural surface. It is found scattered on mossy, steep slopes and in open bogs, occasionally in low-elevation wet forests, primarily in the Ko’olau Mountains of O’ahu and West Maui between 700-1,460 meters.