CARDUUS, in botany, a genus of the syngenesia polygamia æqualis class. The calix is ovated, and imbricated with spinous scales; and the receptacle is hairy. There are 26 species, ten of which are natives of Britain, viz. the lanceolatus, or spear-thistle; the nutans, or milk-thistle; the acanthoides, or warded-thistle; the crispus, or thistle upon thistle; the palustris, or marsh-thistle; the dissectus, or English soft thistle; the helenioides, or melancholy thistle; the marianus, or milk-thistle; and the acaulos, or dwarf carline-thistle.