annatto, (Bixa orellana), tree native to the New World tropics and the only species of the family Bixaceae. Annatto grows up to 9 metres (30 feet) tall and has rose-pink flowers about 5 cm (2 inches) wide and ovate leaves about 8 to 18 cm (3 to 7 inches) long. The brown fruits, about 5 cm (2 inches) long, yield a reddish or yellowish powder that is used in a dye for butter, cheese, and oleomargarine. The plant is cultivated in tropical and subtropical areas of the world.