Senna gaudichaudii is a shrub that ranges in height from 0.5 to 3 (sometimes up to 4) meters, characterized by young parts that are sparsely to densely covered in yellowish pubescent hairs that spread. However, it is occasionally found to be glabrous. The leaves of this plant are compound and alternate, with (3)4–5(6) pairs of opposite leaflets. These leaflets range from oblanceolate to elliptic in shape, with the distal ones being larger, measuring 2–7(–10.5) cm in length and (0.6–)1–1.8(–3.3) cm in width. The apex of each leaflet is typically rounded and emarginate, with an obliquely rounded base. Clavate nectaries, measuring 1–3 mm long, are present between the first and usually second pairs of leaflets. The upper surfaces of the leaflets are green and can be either glabrous or pubescent along the midrib. In contrast, the lower surfaces are glaucous and may be evenly pubescent, only along the midrib, or entirely glabrous. The margins are slightly ciliate, and the stipules are linear-subulate, measuring 6–18 mm in length, and are either deciduous or occasionally persist for a short time. The flowers appear in racemes 2–10 cm long, featuring caesalpinaceous flowers with 11–24 mm long pedicels. The bracts are narrowly ovate to lanceolate, measuring 3–7 mm long, and persist on the plant. The calyx lobes are elliptic-ovate, with the outer ones being 3–4 mm long and the inner ones 5–9 mm long. The corolla comprises five greenish-white petals to chartreuse or pale yellow, occasionally with a red tinge, and are 9–17 mm long. It has ten fertile stamens that are almost similar to one another, with slightly increasing size towards the abaxial side of the flower. The filaments are straight, shorter, and not more than twice as long as the basifixed anthers. The fruit is pendulous, chartaceous, strongly compressed, and measures 6–13 cm long and 1.2–1.5 cm wide. It is indehiscent or tardily, with seeds oriented transversely in a single row, dark reddish-brown, and compressed–ellipsoid in shape, measuring 7–8 mm long. It primarily occupies leeward sites, often on talus slopes, lava flows, or rocky sites within coastal shrubland, disturbed halo forests, dry forests, and occasionally in the lower portions of mesic forests between 5-920 meters.