Diffuse knapweed was introduced from Europe and is a biennial or short-lived perennial forb which reproduces only by seed. It is known to have more than one stem produced from one rosette. A basal rosette of leaves is present in young plants with each leaf divided into narrow segments. When leaves are young, a thin nap is present. Stem leaves in the mature plant become much reduced as you ascend to the tip and alternate one per node.
Flowers are mostly white, sometimes purple, and are located on each branch tip.
The bracts surrounding each flower bear 4 to 5 pairs of lateral spines and one, long terminal spine. Diffuse knapweed can resemble spotted knapweed with the black tipped bracts. The difference is the sharp spine at the end of the bract that is characteristic of diffuse knapweed. Diffuse knapweed can be found in pastures, riparian areas, roadsides, and waste areas in Colorado. It is a tough competitor on dry sites and rapidly invades and dominates disturbed areas.