[Members of the Sunflower Family with Discoid Flower Heads]

Wildflowers of the Genus Centaurea:

Knapweeds of the Columbia River Gorge

Spotted Knapweed: Centaurea stoebe ssp. micranthos (Synonyms: Centaurea biebersteinii, Centaurea maculosa)

Spotted knapweed

The flowers of this species are all discoid, but I have placed them here because the outer ring of corollas may be greatly enlarged, falsely giving them the appearance of having ray flowers to those who don't look closely.

1. Bachelor's Button, Cornflower, Garden Cornflower: Centaurea cyanus - An introduced species, with showy flower heads. The flowers are bright blue, pink, purple, or white.

2. Diffuse Knapweed, Tumble Knapweed, White Knapweed: Centaurea diffusa - An introduced, weedy species. The stems are stiff, erect, and many branched. Flower heads are narrow, one at the end of each branch, with a few white flowers.

3. Spotted Knapweed: Centaurea stoebe ssp. micranthos (Synonyms: Centaurea biebersteinii, Centaurea maculosa) - An introduced, weedy species. The stems are stiff, erect, and many branched. The flower heads are larger than the previous species, with purple-pink flowers. A good diagnostic feature is the dark comb-like bristles at the tips of the involucral bracts.

4. St. Barnaby's Thistle, Yellow Star Thistle, Yellow Star-thistle: Centaurea solstitialis - An introduced, weedy species. The stems are stiff, erect, and many branched. The flower heads have yellow flowers, and distinct, long, straw-colored spines arising from the involucral bracts.


Paul Slichter