Senna includes herbs, shrubs, and trees. The leaves are pinnate with opposite paired leaflets. The inflorescences are racemes at the ends of branches or emerging from the leaf axils. The stamens may be different sizes, and some are staminodes. The fruit is a legume pod containing several seeds.
Senna species are pollinated by a variety of bees, especially large female bees in genera such as Xylocopa.
Sennas have for millennia played a major role in herbalism and folk medicine.
Several Senna species are used as herbal remedies in Nigeria to treat various conditions, including constipation, fungal skin infections, and hemorrhoids
Cassia gum, an extract of the seeds of Chinese senna (S. obtusifolia), is used as a thickening agent.
Senna italica ssp. italica (syn. Cassia obovata), often called neutral henna, is used as a hair treatment.
It has effects similar to henna, but without the red color, giving hair more of a yellow tinge.