SILPHIUM, in botany: A genus of plants belonging to the class of syngenesia, and to the order of polygamia necessaria; and in the natural system arranged under the 49th order, compositæ. The receptacle is paleaceous; the pappus has a two-horned margin, and the calyx is squarrose. There are eight species; the laciniatum, terebinthinum, perfoliatum, connatum, asteriscum, trifoliatum, foldagmoides, and trilobatum. The first six of these are natives of North America.