Pasture thistle

Cirsium undulatum, the wavyleaf or pasture thistle, is a stout biennial or short-lived perennial herb of the Asteraceae family native to the prairies, plains and intermountain regions of central and western North America. It typically grows 30 to 120 cm tall from a deep taproot, with an erect, leafy, white-tomentose stem. The leaves are oblanceolate in outline, deeply pinnatifid to shallowly lobed with spine-tipped lobes and wavy, undulate margins (giving the specific epithet), grey-tomentose on both surfaces. Heads are large, solitary or in small terminal clusters, 4 to 6 cm across, with an ovoid involucre of tightly imbricate, spine-tipped phyllaries and showy pale pink to lavender disc florets only. The achenes are flattened, smooth, dark brown and topped with a long, plumose pappus aiding wind dispersal. It inhabits dry prairies, sagebrush steppe and roadsides on sandy to clayey soils.