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".The genus is confined to North America, with the center of its distribution in California. Some species (e.g. C. americanus) are found in the eastern United States and southeast Canada, and others (e.g. C.