[Members of the Sunflower Family with Discoid Flower Heads East of the Cascade Mountains of Oregon and Washington]

Knapweeds East of the Cascade Mountains of Oregon and Washington

The Genus Centaurea

Spotted knapweed: Centaurea stoebe

The flowers of this species are all discoid although 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.

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

Diffuse Knapweed, Tumble Knapweed, White Knapweed: Centaurea diffusa (Synonym: Acosta 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.

Bighead Knapweed, Globe Knapweed: Centaurea macrocephala -

Maltese Starthistle, Maltese Star-thistle, Napa Thistle, Tocalote: Centaurea melitensis -

Montane Starthistle, Mountain Bluet, Mountain Cornflower, Perennial Cornflower: Centaurea montana (Synonym: Centaurea montana var. alba) -

Black Knapweed, Hardheads, Lesser Knapweed: Centaurea nigra (Synonym: Centaurea nigra var. radiata) -

Short-fringed Knapweed, Tyrol Knapweed: Centaurea nigrescens (Synonyms: Centaurea debeauxii ssp. thuillieri, Centaurea dubia, Centaurea dubia ssp. nigrescens, Centaurea dubia ssp. vochinensis, Centaurea jacea ssp. nigrescens, Centaurea transalpina, Centaurea vochinensis) -

St. Barnaby's Thistle, Yellow Starthistle, Yellow Star-thistle, Yellow Star Thistle: Centaurea solstitialis (Synonym: Leucantha 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.

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

Squarrose Knapweed: Centaurea virgata ssp. squarrosa (Synonyms: Centaurea squarrosa, Centaurea triumfettii, Centaurea variegata, Centaurea virgata var. squarrosa) -

Meadow Knapweed, Protean Knapweed: Centaurea x moncktonii (Synonyms: Centaurea debeauxii, Centaurea debeauxii ssp. thuillieri, Centaurea x pratensis) -

Paul Slichter