Tansy ragwort

Image by: James Altland, USDA-ARS
Terminal flower clusters contain numerous flower heads consisting of both ray and disc flowers.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Tansy ragwort develops a small rosette with distinctly purple petioles early in its first year of growth.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Plants eventually form a small mound 12 to 24 inches tall and wide.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
As plants begin to flower, they generally develop a more upright to columnar form.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Foliage is dark green, typically 2 to 10 inches long, and pinnately or bi-pinnately lobed.
Image by: James Altland, USDA-ARS
Senecio jacobaea
Family: 
Asteraceae
Life cycle: 
Biennial
Habit: 
Tansy ragwort germinates in the fall or early winter. A small rosette forms and lives through the following year. Plants eventually form a small mound with several erect, sturdy stems arising above the foliage on to which flower buds develop. This clump continues to grow through the season. Stems have been known to reach heights up to 6 feet, but more commonly seen are plants between 2-4 feet in height. A large taproot supports this structure.
Flowers: 
Flower heads occur in clusters called corymbs at the terminal end of stems. Long woolly hairs are often observed just beneath flower clusters. Flower heads consist of many bright-yellow ray and disc flowers.
Favorable environments: 
Field
Favorable environment notes: 
Tansy ragwort is found in disturbed areas such as clear cuts, roadsides, and pasture land throughout the Northwest.
Dissemination: 
Tansy ragwort reproduces mainly by seed. Each seed is covered in white pappus which aids in its dispersal by the wind. Seeds can lie dormant in the soil for very long periods of time, reportedly up to 15 years! Seeds can still develop on uprooted plants lying on the ground. If removing by hand or mowing, take care to do so before plants are in bloom.
Of interest: 
Tansy ragwort is toxic to cattle and horses if ingested. Its toxins cause severe and irreversible liver damage. Goats, deer and pigs can also be at risk. The leaves are the most toxic part of the plant.