ARCTIUM, in botany, a genus of the syngenesia polygamia aequalis class. The calix is globular, squamous, and hooked at the tops. There are only two species of arctium, viz. the lappa, or burdock, a native of Britain; and the perfonata, a native of the Alps, &c. The roots and seeds of the lappa are esteemed to be diuretic and sudorific. Decoctions of the roots have of late been used in rheumatic and gouty disorders.