Tumble knapweed

Centaurea diffusa, commonly known as diffuse or tumble knapweed, is a biennial to short-lived perennial herb in the daisy family (Asteraceae). Plants form a basal rosette of deeply pinnately divided, greyish-pubescent leaves in the first year and produce a much-branched, wiry, erect flowering stem 30-100 cm tall in subsequent years; the rounded shape and brittle base allow the entire plant to break off and tumble in the wind, dispersing seed. Stem leaves are alternate, reduced upward, and progressively less divided. Numerous small flower heads are borne on the ends of the branches; each head is 4-6 mm wide with 4-5 mm long involucral bracts ending in a slender, comb-toothed, spiny tip about 2-4 mm long that distinguishes the species. Florets are tubular, typically white to pale pinkish-lavender (rarely purple). Achenes are small, brown, and lack a pappus or have only minute bristles. Native to eastern Europe and western Asia, it is a serious invasive on disturbed rangelands across western North America.