(Cephalanthus), genus of shrubs or small trees of the madder family ( Rubiaceae, q.v.) native to Africa, Asia, and North America. It was named for its fragrant, creamy white, spherical flowers, about 2.5 centimetres (1 inch) in diameter. There are at least 6 species of buttonbush. Cephalanthus occidentalis, the most common, grows about 6 meters (20 feet) high.