Stock Photo - Common Ragwort, Jacobaea vulgaris, a tall plant with bright yellow flowers that resemble daisies on woody stalks. Plant is biennial but seems to be perennial as result of root systems. Hermaphrodite flower heads are 1. 5â. “2. 5 cm in dense clusters. Long flowering period from June-November. Plant is host to many insects including butterflies, moths, bees, hoverflies, etc. Host plant to Cinnabar Moth, Tyria jacobaeae. Must be hand cleared from pasture as toxic to livestock. Critical host plant for 77 insect species, including threatened and endangered species. Toxin in ragwort is cumulative.