Sesbania is an erect annual herb of the legume family that typically grows to a height of 3–10 feet. The base can become woody with age. Its rather large leaves are 4–12 inches long with 20–70 leaflets per leaf. Flowers are 1/2 to 3/4 inch long, yellowish, and strongly speckled with purplish brown.
It has slender, four-sided pods, about 6–8 inches long and 1/8 to 3/16 inch wide, often curved, often tipped with a thin "beak." The seeds are small and numerous, about 1/8 to 3/16 inch long and 1/16 inch wide. The seeds are more or less orange on their attachment side, with the other surface possessing a more or less olive-green background, speckled or blotched with black.