senna, any plant of the genus Sennia (formerly placed in Cassia ), leguminous herbs, shrubs, and trees of the family Leguminosae (pulse family), most common in warm regions. Some species are cultivated for ornament, but sennas are best known as medicinal plants. The dried leaves are used as a purgative and are chiefly obtained from S. acutifolia (Alexandria senna) and S. angustifolia (Indian senna); both trees are cultivated especially in S India. The wild senna ( S. marylandica ), a perennial of the E United States, has been similarly used. Golden shower ( S. fistula ) of India yields canafistula, a purgative extracted from the fruit pulp. The young shoots of several wild species are used for food and the seeds for a coffee substitute. S. nictitans, a North American herb, is sometimes called wild sensitive plant because its leaves respond to touch as do those of the true sensitive plant, a mimosa. Senna is classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Leguminosae.