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; rarely the ray flowers may be absent. 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, appressed to somewhat spreading, green to brown with a brown appendage at the tip that is generally triangular in outline and longer than wide. The lower/outer phyllaries have appendages with up to 15 narrow, comb-like teeth along each edge; the upper/inner phyllaries become less finely divided with thin, papery edging that is irregularly cut or shredded. The phyllary bodies are mostly hidden by the larger appendages. The entire set of phyllaries (involucre) is ½ to ~¾ inch long and about as long as wide.

Leaves and stems:

Leaves are basal and alternate, green, somewhat hairy. Basal and lower stem 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 a few 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. A tuft of hairs at the tip may be absent, or when present the hairs are of unequal lengths and may shed early.

Notes:

Meadow 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. Meadow 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. Meadow Knapweed is a hybrid between Brown Knapweed (Centaurea jacea) and Black Knapweed (C. nigra) and its phyllaries are 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 transform to less finely divided, papery and ragged-edged appendages (similar to Brown Knapweed) on the upper part of the involucre. The phyllary bodies are mostly hidden by the larger appendages. 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.

Meadow Knapweed has also been confused with Alpine Knapweed (C. nigrescens), which has consistently dark brown to black phyllary appendages that are all similar with fewer comb-like teeth, and do not much hide the longer, green phyllary bodies.