Tansy ragwort2017-07-24T20:29:50+00:00

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

USDA Code

SEJA

Legal Status

Colorado Noxious Weed List A

Identification

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

Impacts

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.

 

Biology/Ecology

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

References

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

Back to Weed List