Welted thistle

Carduus acanthoides, the welted thistle, plumeless thistle, or spiny plumeless thistle, is an erect biennial (occasionally annual or short-lived perennial) herb in the family Asteraceae native to Europe and western Asia and now widely naturalized as an invasive weed across temperate North America, especially in the Great Lakes region and the western states. The plant arises in its first year as a flat rosette of leaves and in its second year produces a stout erect branched flowering stem 30-150 cm tall. The stems are conspicuously winged along their length, the wings dissected into broad spiny lobes that extend almost continuously from leaf to leaf and bear stout yellow-tipped spines, the wings giving the plant its English name "welted". Leaves are alternate, oblong-lanceolate in outline, 10-25 cm long, deeply pinnatifid into 6-10 pairs of broadly triangular spiny lobes, the surface sparsely cobwebby above and slightly hairy beneath. The flower heads are borne singly or in small clusters at the branch tips, each 1.5-2.5 cm across with a hemispherical involucre of stiff narrow spine-tipped bracts and a dense tuft of purple to reddish-pink tubular disc florets only (no ray florets). The achenes are smooth and bear a single row of long simple white pappus bristles.