Senicio jacoaea L.
Keys to Identification
- Multiple yellow flowers in inflorescence.
- Stems may be purplish-red.
- Disk flowers have black tips.
Stinking Willie, Tansy Butterweed
Colorado Noxious Weed List A
Biennial or short-lived perennial
Yellow. July-September. Has both ray and disk flowers.
Disk flowers are hairy. Ray flowers are smooth.
2-8 in long. Multi-lobed.
Mature plants 1-6 ft tall. Stems have downy hairs.
Taproot with fleshy side roots.
Senicio sp., Grounsel
Toxic to livestock.
Displaces native vegetation.
Habitat and Distribution
Found in pastures, along rights-of- way and disturbed places. Prefers moist soils.
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.
Tansy ragwort is native to Europe. Known in North America since the early 1900’s.
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.
Produces up to 150,000 seeds.
The majority of the seeds will germinate the following year, but some seeds may remain dormant for several years.
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