Pink, Rose, Red, or Purple Flowered Forbs

Pink, Rose, Red & Purple Flowered Forbs
Black henbane
Blue Mustard
Bull thistle
Canada thistle
Common burdock
Diffuse knapweed
Iberian knapweed
Meadow knapweed
Musk thistle
Purple loosestrife
Purple starthistle
Red clover
Redstem filaree
Russian knapweed
Scotch thistle
Spiny plumeless thistle
Spotted knapweed
Squarrose knapweed
Tall morning-glory


Squarrose Knapweed
Centaurea virgata Lam. ssp. squarrosa (Willd.) Gugler (Aster family, Asteraceae)


Erect, multi-branched perennial forb with a woody base, 20 inches tall, with spiny or comb-like flower head bracts; stoutly taprooted; plants exist as basal rosettes until erect, highly branched flowering stems are produced in late spring/summer.

Leaves: Cotyledons spatulate to oval; rosette leaves pinnate- divided; leaves resin-dotted; upper stem leaves entire, linear or bract- like, mostly lacking at flowering, 3/8 to 3/4 inch long.

Flowers: Flowers June to August; flower heads solitary or several; pink to pale purple flowers average 4 to 8 per head, 1/4 to 3/8 inch long; flower head bracts roughly 1/4 inch long, pale green to straw colored sometimes purple-tinged, spine-tipped; central spine usually reflexed downward to 1/8 inch long.

Fruit: Pale brown achenes oblong, 1/8 to 3/16 inch long, apex flattened and tapered to a rounded, laterally notched base, finely hairy, roughly 2 to 4 per head, pappus bristles less than 1/8 inch long or lacking.


Cultivated and disturbed or degraded rangelands and roadsides within elevations that generally range below 8,000 feet.


Reproduces by seed, germination can occur over a broad range of environmental conditions; seedling emergence is typically highest after the first fall rains; mortality of seedlings that emerge in spring can be high when conditions become dry after emergence; most seedlings emerge from seeds at or near the soil surface; plants produce fewer viable seeds in dry years; infestation density correlates with the age of the population and degree of disturbance.


Native to Asia; squarrose knapweed is a very competitive and aggressive plant with allelopathic effects; stands of squarrose knapweed may persist indefinitely once established. Arizona prohibited noxious weed.

Collage of images or squarrose Knapweed


Forest Service Shield
Invasive plants and weeds of the national forests and grasslands in the southwestern region
Squarrose knapweed flower heads Squarrose knapweed flower weeds Squarrose knapweed plants Squarrose knapweed foliage