Cassia is a genus of flowering plants in the legume family, Fabaceae, and the subfamily Caesalpinioideae. Species are known commonly as cassias. The genus includes 37 species and has a pantropical distribution. Species of the genera Senna and Chamaecrista were previously included in Cassia. Cassia now generally includes the largest species of the legume subtribe Cassiinae, usually mid-sized to tall trees.

Caesalpinioideae is a botanical name at the rank of subfamily, placed in the large family Fabaceae or Leguminosae. Its name is formed from the generic name Caesalpinia. It is known also as the peacock flower subfamily. The Caesalpinioideae are mainly trees distributed in the moist tropics, but include such temperate species as the honeylocust and Kentucky coffeetree. It has the following clade-based definition:The most inclusive crown clade containing Arcoa gonavensis Urb. and Mimosa pudica L., but not Bobgunnia fistuloides (Harms) J. H. Kirkbr. & Wiersema, Duparquetia orchidacea Baill., or Poeppigia procera C.Presl