State Noxious Weed List -Yes (both species)

Growth form: Both are short-lived perennials or sometimes biennial plants reproducing solely by seed. The plants grow 2 to 4 feet tall with one or more stems. The leaves are pale green and 3 to 4 inches long.

Rosette leaves are deeply lobed. The physical appearance of these two knapweed species is similar, except diffuse knapweed is generally shorter and more highly branched. Plants flower from early July through August and produce 1000 or more seeds per plant.

These species are distinguished by the bracts below the flower. Spotted knapweed has stiff, black-tipped bracts while diffuse knapweed has a rigid terminal spine about one-third of an inch long with four to five pairs of shorter, lateral spines (crab like). Both species have pink to light purple and occasionally white flowers.