Smooth Rattlepod is a perennial herb or subshrub, with stems ascending or erect, 1-2 m tall. Leaves are trifoliate, leaflets elliptic, ovate, or oblanceolate, 2.8-9.5 cm long, 1.2-4.5 cm wide. Leaf base is wedge-shaped or rounded, with leaf stalk 2.2-6.7 cm long. Flowers are 1-1.5 cm long, 22-75 in terminal, somewhat lax inflorescences about 15-40 cm long. Petals are yellow with lines near base, standard petal 0.9-1.2 cm long, 7-9 mm wide, keel petals striate, with nontwisted prolonged beak. Pods brown at maturity, 3.5-3.8 cm long.