Peucedanum sandwicense is a perennial herb that exhibits a robust, erect, or sprawling growth form, ranging from 50 to 200 cm in height and is characterized by a glabrous and glaucous surface. The stems are caulescent, supporting the plant’s structure and growth. It features compound leaves that are either pinnate or ternate-pinnate and arranged alternately along the stem. The basal leaves are similar in form to the cauline leaves but reduce in size upwards, with the larger leaves often 1–3-lobed, measuring 7–13 cm in length and 2.5–7 cm in width. The leaflets are ovate-lanceolate to orbicular, reaching 10–35 cm long dimensions. These leaves have subacute to obtuse apices and truncate to obliquely cuneate bases, with serrated or serrate-dentate margins that are palmately veined. The stout petioles range from 10 to 50 cm, sheathing narrowly at the base, and are devoid of stipules. The flowers are arranged in a fertile terminal umbel, accompanied by one or more staminate, lateral, axillary umbels. The terminal peduncle is stout, 10–20 cm long, sometimes accompanied by deciduous or absent linear-oblong to lanceolate bracts up to 2 cm long. The umbels consist of 15–25 rays that are spreading-ascending and 5–8 cm long, leading to umbellets that contain 10–20 flowers each. The polygamous flowers display a mix of unisexual and bisexual forms on the same plant. Notably, the pedicels are spreading-ascending, 5–12 mm long, and webbed. The calyx lobes are ovate and persistent, measuring approximately 2.5 mm. The corolla comprises five orbicular white petals with inflexed narrower apices. It has five stamens, an inferior ovary with two cells, and two styles swell at the base into a conical stylopodium that exceeds the short styles. The fruit is oblong to oblong–ovoid, measuring 10–13 mm in length and 5–8 mm in width. The mericarps are dorsally flattened and glabrous, with low, rounded dorsal ribs and broadly winged lateral ones. One per mericarp, the seeds are encased in a cartilaginous endosperm and have lanceolate cotyledons. It is found on windward cliffs up to 250 meters.