Europe, Siberia, and Asia
Tansy ragwort is an herbaceous biennial (sometimes a winter annual or short-lived perennial) typically growing 1–3 ft (30– 90 cm) tall. The root system consists of one to several soft, fleshy roots. Leaves are deeply lobed to pinnately toothed, alternate, and 3–8 in (7½–20 cm) long. Stems arise singly or in clumps and branch near the top with multiple flower heads. Flowering occurs from July to September. Flower heads consist of yellow disc (center) and ray (outer) florets. Ray florets (usually 13) resemble petals and grow S–¾ in 8–20 mm long. Seeds are topped by a fine pappus.
Tansy ragwort displaces native species in natural areas and reduces range and pasture production. All parts of the plant contain pyrrolizidine alkaloids that are responsible for livestock fatalities, contaminating milk production, and the tainting of honey made from tansy ragwort nectar. Many people are also allergic to this weed.
Szqcs, M., J. Littlefield, C.B. Randall, and J.E. Andreas. 2022. Tansy Ragwort (Jacobaea vulgaris): History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2022-21-TANSY RAGWORT-P. https://bugwoodcloud.org/resource/files/25373.pdf