Weed of the Week

3-3-08

Spotted Knapweed, Centaurea maculosa

             

Photo credits: (c) John M. Randall/The Nature Conservancy Washington State Weed Control Board

 Characteristics:

Family: Asteraceae (Sunflower family)

Origin: Eurasia

Description:

• Biennial or short lived perennial with a stout taprootVery showy flowers

Stems:

• 1 or more stems

• 1-3 feet tall

 

Flowers:

• Singular at the end of the branch

• Pinkish-purple in color

• Bracts under the flower head are tipped with dark spots and fringes

Leaves:

• Stem leaves inconspicuous and pinnately divided

• Basal leaves larger up to 6" and pinnately divided

Fruit:

• 1/8" long tipped with a tuft of persistent bristles

Additional information:

Introduced as a contaminant in alfalfa and clover seed and is the number one weed problem in Western Montana.  Spotted knapweed easily establishes itself on any disturbed soil and their early Spring growth makes them extremely competitive with other plants.  There is evidence that Spotted knapweed is allelopathic, emitting chemicals to inhibit other plant growth.  Flowering period is from June to October.

---

Return to Weed of the Week Page

Return to Park Operations Page

---