PO Box 419

Hotchkiss, CO 81419



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Tansy ragwort

Senicio jacoaea L.


Keys to Identification

  • Multiple yellow flowers in inflorescence.
  • Stems may be purplish-red.
  • Disk flowers have black tips.

Family: Sunflower (Asteraceae)


Other Names: Stinking Willie, tansy butterweed




Legal Status: Colorado Noxious Weed List A




Lifecycle: Biennial or short-lived perennial


Growth form: Forb


Flower: Yellow. July-September. Has both ray and disk flowers.


Seeds/Fruit: Disk flowers are hairy. Ray flowers are smooth


Leaves: 2-8 in long. Multi-lobed


Stems: Mature plants 1-6 ft tall. Stems have downy hairs.


Roots: Taproot with fleshy side roots



Similar Species

Exotics: None known.


Natives: Senicio sp., Grounsel




Agricultural: Toxic to livestock


Ecological: Displaces native vegetation



Habitat and Distribution

General requirements: Found in pastures, along rights-of- way and disturbed places. Prefers moist soils


Distribution: Found in California, Idaho, Illinois, Maine, Massachusetts, Michigan, Montana, New Jersey, New York, Oregon, Pennsylvania, Washington. Recently found in Alaska. Not known to occur in Colorado.


Historical: Tansy ragwort is native to Europe. Known in North America since the early 1900's.




Life cycle: Tansy ragwort generally produces a basal rosette the first year, and flowers the following year. The plants are prolific bloomers and produce large quantities of seed from July through September.


Mode of reproduction: Seed. May sprout from root fragments.


Seed production: Produces up to 150,000 seeds.


Seed bank: The majority of the seeds will germinate the following year, but some seeds may remain dormant for several years.


Dispersal: Wind





Whitson, T.D.(ed.), L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, R. Parker. 2001. Weeds of the West. Western Society of Weed Science, in cooperation with the Western United States Land Grant Universities Cooperative Extension Services, Newark CA.


Growers Weed Identification Handbook, University of California Publication 4030, pg. WI-212


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