Jacobaea vulgaris aka Jacobaea

Jacobaea vulgaris is highly adaptable and tolerates virtually any soil type including light sandy, medium loamy, and heavy clay soils. It succeeds on most soils except the very poorest and can grow in nutritionally poor conditions. The plant accepts acidic, neutral, and alkaline pH levels, making it extremely versatile in soil requirements.

Jacobaea vulgaris propagates readily from seed, producing thousands of seeds per plant. Seeds germinate in 2-3 weeks at 18-22°C and require light for germination. Seeds should be surface-sown and watered from below as seedlings are easily damaged. The plant produces two types of seeds: those in the flower center have hair for wind dispersal, while outer seeds are heavier and drop locally. Seedlings typically appear in autumn and form overwintering rosettes.

Jacobaea vulgaris typically reaches 0.3-1.0 meters tall with a spread of 0.5-1.0 meters, though it can occasionally reach up to 1.5 meters in favorable conditions. It grows with a clump-forming, columnar upright habit. As a biennial or short-lived perennial, it forms a low rosette in the first year, then produces upright flowering stems in the second year. The plant has a fast growth rate and spreads readily through prolific seed production.

Jacobaea vulgaris is native to northern Eurasia, specifically Europe (including Britain), North Africa, the Caucasus, and Western Asia. It thrives in temperate climates and is commonly found in its native range on roadsides, waste grounds, railway embankments, meadows, and pastures. The plant has since spread globally and become invasive in regions including North America, Australia, and New Zealand.

Jacobaea vulgaris produces large, flat-topped clusters of bright yellow, daisy-like flowers from mid-summer to mid-autumn (June through October). Each flower head is 15-25 millimeters in diameter with yellow ray florets surrounding small tubular disk florets. The flowers grow in dense corymbs at the stem tops and are highly attractive to pollinators including bees, flies, and butterflies. Seeds ripen from July to October following flowering.

Jacobaea vulgaris is pollinated by a variety of insects including bees, flies, and Lepidoptera (moths and butterflies). The plant is hermaphroditic and self-fertile, but primarily relies on insect pollinators attracted to its bright yellow daisy-like flowers. It is particularly noted for attracting wildlife and serves as an important nectar source for numerous pollinator species throughout its long flowering period from June to October.

Jacobaea vulgaris is relatively resilient to most pests due to its toxic alkaloid content, but specialized insects have adapted to feed on it. The cinnabar moth (Tyria jacobaeae) larvae are the most notable pest, with caterpillars that can consume entire plants. The tansy ragwort flea beetle (Longitarsus jacobaeae) feeds on root crowns, and seed flies attack seeds. These insects have evolved to tolerate the plant's toxins and are sometimes used as biological control agents. The plant may also be affected by rusts and fusarium wilt.

Jacobaea vulgaris is exclusively an outdoor plant hardy in USDA zones 4-8 and UK hardiness zone 5 (H7). It thrives in full sun with south or west-facing exposure and tolerates severe European continental climates. However, cultivation is strongly discouraged as it is a declared noxious weed in many regions including Britain, Australia, and New Zealand. In areas where it is invasive, landholders may be legally required to remove it due to its toxicity to livestock and aggressive spreading habit.

Jacobaea vulgaris follows a biennial growth pattern requiring minimal care. Seeds germinate in autumn, forming overwintering rosettes of deeply lobed leaves in the first year. In the second year, the plant produces upright flowering stems from late spring through summer, blooming June to October. Where the plant is unwanted, control measures should be implemented before flowering or when flowers first open, as each plant produces thousands of seeds. The rosette stage is the best time for removal.

Jacobaea vulgaris is not edible - all parts of the plant are poisonous to humans. It contains toxic pyrrolizidine alkaloids including jacobine, ridelliina, senecionine, and seneciphylline that cause cumulative liver damage. There are no known edible uses for this plant, and consumption can result in severe hepatotoxicity. The plant should never be consumed or used in food preparation.

Jacobaea vulgaris has historical medicinal uses but is extremely dangerous and should only be used under expert supervision if at all. Traditionally used as an astringent, diaphoretic, diuretic, emmenagogue, and expectorant for treating dysmenorrhoea and internal hemorrhages. However, when taken internally it causes severe liver damage due to pyrrolizidine alkaloids. External poultices for wounds may be safer, though some people develop skin rashes from contact. Modern herbalism generally avoids this plant due to hepatotoxicity risks.

Jacobaea vulgaris serves primarily as a natural dye source and wildlife plant. The leaves yield green dye (though not permanent), flowers produce yellow dye with alum mordant, and brown and orange colors are also obtainable. Ecologically, it is the main food plant for cinnabar moth caterpillars and provides nectar for numerous butterfly and moth species. The plant serves as an exclusive food source for ten rare or threatened insect species in its native range, creating important conservation value despite its invasive status elsewhere.

Jacobaea vulgaris has several recognized subspecies including subsp. vulgaris (the typical form), subsp. dunensis found in dune habitats, and subsp. gotlandica from Gotland. These subspecies show adaptations to different habitats within the species' broad native range across Europe and Asia. While there is variation in alkaloid content and morphology between populations from the same location, these are generally not recognized as distinct cultivated varieties.