in botany, a genus of the polygamia dioica clas. The umbella of the male is compound; the involucrum consists of five leaves; the corolla has five petals; the flamina are five; and two pistils: The umbella of the hermaphrodite is simple; the involucrum is divided into four parts, is spinous, large, and contains many male flowers in the disk. There is but one species of arctopus, viz. the echinatus, a native of Ethiopia.