Centaurea diffusa L.
Diffuse knapweed, a member of the sunflower family, is originally from the Mediterranean Region. It is a biennial or short-lived perennial forb which reproduces only by seed. Each leaf is divided into narrow segments, and young leaves are covered in thin hairs. The stems and leaves are rough to the touch. Fully grown, it is 1-1/2 to 3 feet tall, usually producing a single main stem with numerous branches. Stem leaves in the mature plant become reduced nearer to the tip and alternate one per node. Flowers are mostly white to pink, rarely 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. Flowering occurs from July to September.
Diffuse knapweed can be found in pastures, riparian areas, roadsides, and waste areas. It is a tough competitor on dry sites and rapidly invades and dominates disturbed areas. Diffuse knapweed can resemble spotted knapweed, but the easiest difference is spotted knapweed’s dark-outlined bracts; also, diffuse knapweed’s bracts have distinct spines.
If you find this weed on your property or around Teton County, please report it immediately at 733-8419.