Squarrose Knapweed (Centaurea virgata ssp. squarrosa)

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Squarrose knapweed is a long-lived perennial with deep tap roots. Rosette leaves are deeply lobed and gray-green. The stems are upright, stiff, winged 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. Plants range in height from 15 to 60 cm. Flower heads with 4 to 8 pink or purple flowers are borne singly or in pairs at the tips of branches. The seed heads are small and covered with spiny bracts having a long, recurved (backward pointing) terminal spine. The heads are deciduous, falling off the stems after the seeds mature.

Key Identifiers
  • Squarrose is similar to diffuse knapweed but has fewer (4-8) pink to purple flowers per head and recurved spines on the bracts
  • 4-6 pairs of lateral spines, under terminal spine
  • Stout taproot
  • Stalked, deeply lobed basal leaves often wither at flowering time
Location in Canada
No known locations of Squarrose Knapweed in Canada.

California Dept Food & Agriculture

Molly Elizabeth Bagley, California Dept Food & Agriculture

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 squarrose knapweed. The key feature for differentiating all knapweeds from one another is to compare the unique bracts. The 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, leaves and stems of squarrose knapweed lack spines.

Other Documents in the Series

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Squarrose Knapweed (Centaurea virgata ssp. squarrosa) - Current Document
Sulphur Cinquefoil (Potentilla recta)
Tansy Ragwort (Jacobaea vulgaris/Senecio jacobaea)
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For more information about the content of this document, contact Chris Neeser.
This document is maintained by Shelley Barkley.
This information published to the web on April 2, 2012.
Last Reviewed/Revised on August 21, 2018.