Flower:

Thistle-like flower heads 1 to 1½ inches across, single at the ends of branching stems. Each head consists of set of ray flowers around the outer edge and numerous, shorter disk flowers in the center. Ray flowers are sterile, widely spreading, narrowly tubular with 5 slender lobes as long as or longer than the tube. Disk flowers are fertile, erect to ascending, with a column of white-tipped stamens and a divided style. Flower color ranges from pink to purple, occasionally white, with the center disk flowers sometimes much paler than the outer flowers.

The bracts (phyllaries) surrounding the base of the flower are in several layers, mostly appressed, green to brown with a brown appendage at the tip that is roundish in outline, mostly wider than long, with thin, lighter brown, papery edging that is irregularly cut or shredded. The phyllary bodies are short and hidden by the appendages. The entire set of phyllaries (involucre) is ½ to ~¾ inch long and about as long as wide.

Leaves and stems:

Leaves are alternate, green, somewhat hairy. Near the base of the plant leaves may be stalked, up to 10 inches long and 1 inch wide, often widest above the middle, sometimes with a few lobes or teeth, becoming progressively smaller, more lance-elliptic, unlobed and stalkless as they ascend the stem.

Stems are erect to ascending, single or multiple from the base, branched in the upper plant, ribbed, rough textured to sparsely covered in cobwebby hairs.

Fruit:

Fruit is a dry seed, elliptic, brown, finely hairy, 2.5 to 3 mm long that usually lacks a tuft of hairs at the tip.

Notes:

Brown Knapweed is a relative newcomer to Minnesota and is currently on the Eradicate list along with several other Centaurea species, none of which are native to North America. Brown Knapweed flowers are very similar to other Knapweeds with pink to purple flowers, but the phyllaries are fairly distinctive for each species, especially the appendage at the tip of each phyllary. Brown Knapweed phyllary appendages are light to medium brown, mostly wider than long, fairly rounded in outline with paler, papery edging that is more ragged or shredded than toothed. The phyllary bodies are short and hidden by the larger appendages.

Brown Knapweed is very similar in most respects to Meadow Knapweed (Centaurea ×moncktonii), a hybrid between Brown Knapweed and Black Knapweed (C. nigra) and has phyllaries intermediate between the two: phyllary appendages lower on the involucre are triangular in outline with many narrow, regular, comb-like teeth around the edges (which are more similar to Black Knapweed), then gradually transform to less finely divided, papery and ragged-edged appendages (similar to Brown Knapweed) on the upper part of the involucre. Black Knapweed isn't known to be in Minnesota at this time but has been recorded in Wisconsin so it is only a matter of time before it arrives here.