Spotted Knapweed (Centaurea stobe ssp. micranthos)

 
 
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Description
A winter-hardy, short-lived perennial with deep taproots. Plants grow 15 to 60 cm in height. The basal leaves are up to 20 cm long, deeply lobed, and arranged in a rosette. Stem leaves, arranged alternately, are smaller and not lobed. Uppermost leaves are bract-like. The stems are upright, stiff, and branched. Small plants usually have an unbranched stem and one flower head; large plants have a stem with many branches and can have over 100 flower heads. The 5 to 10 mm long flower heads occur singly or in clusters at the branch tips. Each head bears stiff bracts, which are black-tipped, giving the plant its ‘spotted’ appearance. Heads contain from 30 to 50 pink or purple colored flowers.

Key Identifiers
  • Rosette leaves can be 6 inches long and deeply lobed.
  • Pink or purple flowers
  • The mid-stem leaves are pinnately lobed to pinnately compound, as leaves move up the stem they become less dissected and much smaller
  • Edge of bract has a comb-like fringe. Fringes of bracts short, drawn out and rigid, bract with brown/black triangular tip
  • Heads persist on the stiff stems through the winter

Nicole Kimmel, ARD
Location in Canada
BC, NB, NS, Ontario, Quebec and Alberta are all known to have populations of spotted knapweed.

Resources
Pacific Northwest Extension Publication - Identification of Knapweed and Starthistles in the Pacific Northwest

Similar species
(Centaurea spp.) Other knapweeds are going to be similar to spotted knapweed. The key feature for differentiating all knapweeds from one another is to compare the unique bracts. The first link under “Resources” is an excellent resource to walk you through identifying knapweeds.

May be mistaken for a thistle at a passing glance but upon inspection, all parts of spotted knapweed lack spines.
 
 
 
 

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For more information about the content of this document, contact Nicole Kimmel.
This document is maintained by Shelley Barkley.
This information published to the web on April 2, 2012.
Last Reviewed/Revised on March 21, 2014.