Spotted knapweed is a member of the Asteraceae or sunflower family. Spotted knapweed can grow 1 to 3 feet tall. Basal rosette leaves are borne on short stalks and grow up to 6 inches long. Rosette leaves are deeply divided into lobes on both sides of the center vein. Spotted knapweed stems can have more than one stem and are branched on the upper half. Stem leaves are alternate, sessile, and have few lobes, or they are linear and entire, and are smaller toward the uppermost part of the stem. Flower heads are born solitary or in clusters of two or three and are found at the branch ends. Flower heads are ovate to oblong and are pinkish-purple or, rarely, cream colored. Bracts of the plant surround the flower head and are yellow-green to brown in color. The center spine of the bracts is shorter than the lateral spines. Spotted knapweed has obvious longitudinal veins and black-tipped bracts that give the flower head a spotted appearance. Spotted knapweed seeds are brown to black in color, oval in shape, about 1/8 inch long, and tipped with a tuft of bristles.

Spotted knapweed is considered a noxious weed under North Dakota state law, thus landowners are required to eradicate or control the spread of the plant.