Flowers are white to rose in color. Diffuse knapweed differs from squarrose knapweed in that toothed flower bracts are straight rather than arched outward. It blooms throughout summer.
Native to Eurasia, diffuse knapweed inhabits dry rangeland, roadsides, field edges, and waste areas. Knapweed's release chemical substances into the soil that inhibit the growth of competing vegetation.