ZANTHOXYLUM, the TOOTHACHE-TREE, in botany; a genus of plants of the class of diancia, and order of pentandria; and in the natural system arranged under the 46th order, Hederacea. The calyx is quinquepartite; there is no corolla; the female flower has five pistils and as many monospermous capsules. There are two species, the clava herculis, and the trifoliatum; neither of which are natives of Britain.