Ceanothus L. /ˌsiːəˈnoʊθəs/ is a genus of about 50–60 species of nitrogen-fixing shrubs or small trees in the family Rhamnaceae. Common names for members of this genus are California lilac, wild lilac, and soap bush. "Ceonothus" comes from a Greek word meaning "spiny plant", Ancient Greek: κεάνωθος (keanōthos), which was applied by Theophrastus (371–287 BC) to an Old World plant believed to be Cirsium arvense.