Ontario Weeds: Tansy ragwort

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Excerpt from Publication 505, Ontario Weeds, Order this publication

Table of Contents

  1. Name
  2. Other Names
  3. Family
  4. General Description
  5. Stems and Roots
  6. Flowers and Fruit
  7. Habitat
  8. Caution
  9. Similar Species
  10. Related Links

Name: Tansy ragwort, Senecio jacobaea L.,

Other Names: séneçon jacobée, Stinking Willie, herbe de Saint-Jacques, jacobée

Family: Composite or Aster Family (Compositae

General Description: Biennial or short-lived perennial closely related to Common groundsel.

Photos and Pictures

Tansy ragwort.

Tansy ragwort. A. Lower portion of plant.
Tansy ragwort. A. Lower portion of plant.
B. Top of flowering stem.
B. Top of flowering stem.

Stems & Roots: It is usually a taller plant (20-100cm, 8-40in.) with leaves broader in outline and cobwebby-hairy below, more finely divided, not as fleshy, and with their surfaces curled or crisped and wavy like leaf lettuce.

Flowers & Fruit: Flower heads in a short, broad, nearly flat-topped cluster at the end of the stem; each head with several, small, yellow ray florets 4-8mm (1/6-1/3in.) long, a dense centre of yellow disk florets, and with involucral bracts darker green but not black at their tips. Its odour is considered unpleasant by many people. Flowers from July to October.

Habitat: Tansy ragwort occurs in only a few isolated localities in southern Ontario in pastures, waste places, along roadsides, and occasionally in gardens and lawns.

Caution: It is poisonous to livestock and is responsible for Pictou disease of cattle, a serious problem in Nova Scotia where the weed is widespread.

Similar Species: It is distinguished by its deeply dissected leaves with curled or wavy surfaces, its erect stature with somewhat flat-topped inflorescences and its flower heads with yellow rays and yellow centres.

Related Links

... on general Weed topics
... on weed identification, order OMAFRA Publication 505: Ontario Weeds
... on weed control, order OMAFRA Publication 75: Guide To Weed Control

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For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 01 June 2000
Last Reviewed: 01 November 2003