Pink, Rose, Red, or Purple Flowered Forbs

Pink, Rose, Red & Purple Flowered Forbs
Alfalfa
Black henbane
Blue Mustard
Bull thistle
Canada thistle
Common burdock
Diffuse knapweed
Hounds-tongue
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
Teasel

 

Scotch Thistle
Onopordum acanthium L. (Aster family, Asteraceae)
 

Description

Vigorous biennial or short-lived warm-season perennial forb with coarse, spiny leaves and conspicuous spiny-winged stems; 1-1/2 to 12 feet tall.

Leaves: Stems wings, spiny, continuous, and conspicuous, 3/4 to 1-1/4 inches wide; leaves alternate, spiny; leaves covered with gray-white woolly hairs, with the lower surface more densely covered than the upper; leaves 4 to 20 inches long, broadly elliptic; margins spiny-toothed to shallow spiny-lobed.

Flowers: Flowers June to September; flower heads are numerous mostly solitary but sometimes in clusters of 2 to 7, 1 to 2 inches in diameter, flowers white to purple; flower head bracts spine-tipped, less than 1/8 inch.

Fruit: Achenes narrowly obovate, more or less 4- or 5-angled, glabrous, and mottled brown to blackish; surface roughened with wavy transverse ridges, less than 1/8 inch long; pink to reddish pappus bristles equal, numerous, minutely barbed, fused into a ring at the base which separates as a unit, 5/16 to 7/16 inch long.

Habitat

Cultivated and disturbed or degraded moist sites in meadows, grassland, woodland, and riparian communities, and roadsides; within elevations that generally range below 7,500 feet.

Propagation/Phenology

Reproduces only by seed; plants can produce an average of 20,000 to 40,000 seeds; most seeds germinate in fall after the first rains, but some seeds can germinate year round under favorable moisture and temperature conditions; buried seed can remain viable in the soil seed bank for at least 7 years and possibly to 20 years or more; yearly seed production and seed dormancy are highly variable depending on environmental conditions.

Comments

Native to Europe and the Mediterranean region; severe infestations can form tall, dense, impenetrable stands, especially in fertile soils. Arizona prohibited/restricted noxious weed, New Mexico Class A noxious weed, and Oklahoma noxious weed.

Collage of images for Scotch Thistle

 

Forest Service Shield
Invasive plants and weeds of the national forests and grasslands in the southwestern region
Scotch thistle flower head and winged stems Scotch thistle flower heads Scotch thistle foliage Scotch thistle plant