Cassia siamea is an evergreen, flowering multi-trunked, large perennial shrub or small to medium-sized tree. Grows to between 5-13m tall with a 7m spread and a 20-30cm trunk diameter. Straight trunk initially, becoming crooked with age and develops rounded or irregular, spreading multi-branched crown with dense foliage and an open habit, drooping with age. Notes as growing up to 30m tall with a 50 cm trunk diameter in its native habitat. Leaves are glossy dark green with a paler underside.
Flowers are fairly showy, 2.5-3.5cm wide, bisexual, yellow. Seeds are round to obovate, flattened, 6.5-9mm long by 5.5 – 6mm wide, dark brown, smooth and shiny. Fruits at 5 years old. Ornamental tree. Used as a pioneer plant or soil stabilizer in shelterbelts as a windbreak tall hedge and for erosion control. Used as on streets and avenues and overstorey plants. Fast-growing.