Woolly Burdock (Arctium tomentosum)

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Woolly Burdock is a tall biennial, reaching as much as 2.5 m. The fleshy tap-root can grow up to 1m long. The stout, grooved, rough stem has multiple branches. Basal leaf stems are hollow or solid. It has large (up to 40 cm) alternating, heart shaped leaves that have a long petiole, very wavy margins and are pubescent on the underside. The flowers are purple and grouped in globular flower head, united in clusters. The flower head is surrounded by a whorls of bracts, each curving to form a Velcro like hook, allowing them to be carried long distances on the fur of animals. Bracts are densely cobwebby.

Key Identifiers
  • Large plant and leaves
  • Lower leaf stalks are both hollow and solid
  • Whorl of cobwebby bracts under 2.5 cm in diameter
  • Long stalked flowers
  • Flowers clumped along stem with branches in groups
  • Velcro like hooks on bracts

Great Burdock, Lesser Burdock, Woolly Burdock
Location in Canada
Lesser Burdock occurs in all Canadian Provinces from Newfoundland to Alberta. Sometimes grown for medicinal purposes.

Invasive Plant Atlas of the United States - Woolly Burdock

Similar species
Great Burdock (Arctium lappa) lower leaf stalks are solid and flower heads are more than 2.5 cm across
Lesser Burdock (Arctium minus) flowers heads are usually sessile to short stems with very few branches and the flower heads are less than 2.5 cm across

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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 March 30, 2012.
Last Reviewed/Revised on August 21, 2018.