Description

Multi-stemmed perennial forb, 9 to 39 inches tall; openly branched stems covered with cobwebby, matted hairs; creeping rhizomes scaly, dark brown to black; root system branches frequently with individual roots reaching 25 feet in depth; stems with numerous branches; Russian knapweed is similar in appearance to other knapweeds and star-thistles; however, Russian knapweed has rounded to pointed membranous margins whereas flower head bracts of other knapweeds and star-thistles are tipped or fringed with short spines.

Leaves: Basal and cauline (along the stem), simple, alternate; upper cauline leaves narrowly lanceolate to linear, 1/8 to 1/2 inch long, margins entire or toothed; lower cauline leaves often serrate; basal leaves lobed and gray pubescent.

Flowers: Flowers June to September; pink to purplish flower heads range from one to numerous, rising at the end of branches, arranged in a flat-topped to panicle-like inflorescence; flower head bracts arranged in 6 to 8 rows.

Fruits: Oblong achene (fruit), 1/8 to 1/4 inch long; deciduous pappus (tuft-like appendage) at end of achene, whitish bristles unequal, 1/8 to 3/8 inch long, barbed toward the base, feathery toward the tip.

Habitat

Cultivated areas and disturbed or degraded sites in meadows, grassland and riparian communities, and roadsides; establishes in many soil types within elevations that generally range from 3,000 to 8,000 feet.

Propagation/Phenology

Reproduces primarily by vegetative shoots from rhizomes although individual plants can produce small quantities of viable seed. Seed can remain viable 2 to 3 years. Severed roots can produce new shoots from a depth of up to 6 inches.

Comments

Native to central Asia; Russian knapweed is a very competitive and aggressive plant with allelopathic effects; stands may persist indefinitely once established. Arizona prohibited/restricted noxious weed and New Mexico Class B noxious weed.