NOXIOUS WEED
CO, NM, UT

Centaurea diffusa.  Synonym: Acosta diffusa. (Knapweed)    
Asteraceae (Sunflower Family)

Foothills, montane.  Meadows, disturbed areas.  Summer.
Disappointment Valley, June 26, 2011.

There are nearly 400 species of this genus centered in the Mediterranean region.  A number of species are now widespread noxious weeds in the United States. 

The plant is very attractive with numerous bright flowers in plants to two feet tall.  The plants may be annuals, biennials, or, as in the case of the plant shown on this page, short-lived perennials.  Centaurea diffusa occurs along roadsides and other disturbed areas from about 5,000 to 8,000 feet in elevation.

Adanson named the Acosta genus in 1763 and Weber believes this genus name takes precedence over the more generally accepted genus name, Centaurea, given by Linnaeus in 1753.  The species was named Acosta diffusa by Sojak and the C. diffusa species name was given by Jean Lamarck in 1785.

Centaurea diffusa.  Synonym: Acosta diffusa. (Knapweed)    
Asteraceae (Sunflower Family)

Foothills, montane.  Meadows, disturbed areas.  Summer.
Disappointment Valley, June 26, 2011.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Centaurea diffusa