The plant is generally considered to be biennial but it has the tendency to exhibit perennial properties under certain cultural conditions (such as when subjected to repeated grazing or mowing). The stems are erect, straight, have no or few hairs, and reach a height of 0.3–2.0 metres (1 ft 0 in–6 ft 7 in). The leaves are pinnately lobed and the end lobe is blunt. The many names that include the word "stinking" (and Mare's Fart) arise because of the unpleasant smell of the leaves. The hermaphrodite flower heads are 1.5–2.5 centimetres (0.59–0.98 in) diameter, and are borne in dense, flat-topped clusters; the florets are bright yellow. It has a long flowering period lasting from June to November (in the Northern Hemisphere).
Pollination is by a wide range of bees, flies and moths and butterflies. Over a season, one plant may produce 2,000 to 2,500 yellow flowers in 20- to 60-headed, flat-topped corymbs. The number of seeds produced may be as large as 75,000 to 120,000, although in its native range in Eurasia very few of these would grow into new plants and research has shown that most seeds do not travel a great distance from the parent plant.
Two subspecies are accepted:Jacobaea vulgaris ssp. vulgaris - the typical plant, with ray florets present.
Jacobaea vulgaris ssp. dunensis - the ray florets are missing.
Ragwort is abundant in waste land, waysides and grazing pastures. It can be found along road sides, and grows in all cool and high rainfall areas.
Ragwort is native to the Eurasian continent. In Europe it is widely spread, from Scandinavia to the Mediterranean. In Britain and Ireland it is listed as a weed. In the United States it has been introduced, and is present mainly in the northwest and northeast: California, Idaho, Illinois, Maine, Massachusetts, Michigan, Montana, New Jersey, New York, Oregon, Pennsylvania, and Washington.
In South America it grows in Argentina, in Africa in the north, and on the Asian continent in India and Siberia. It is widespread weed in New Zealand and Australia. In many Australian states ragwort has been declared a noxious weed. This status requires landholders to remove it from their property, by law. The same applies to New Zealand, where farmers sometimes bring in helicopters to spray their farms if the ragwort is too widespread.
Ragwort is a food plant for the larvae of Cochylis atricapitana, Phycitodes maritima, and Phycitodes saxicolais. Ragwort is best known as the food of caterpillars of the cinnabar moth Tyria jacobaeae. They absorb alkaloids from the plant and become distasteful to predators, a fact advertised by the black and yellow warning colours. The red and black, day-flying adult moth is also distasteful to many potential predators. The moth is used as a control for ragwort in countries in which it has been introduced and become a problem, like New Zealand and the western United States. In both countries, the tansy ragwort flea beetle (Longitarsus jacobaeae) has been introduced to combat the plant. Another beetle, Longitarsus ganglbaueri, also feeds on ragwort, but will feed on other plants as well, making it an unsuitable biological control.
In the United Kingdom, where the plant is native, ragwort provides a home and food source to at least 77 insect species. Thirty of these species of invertebrate use ragwort exclusively as their food source and there are another 22 species where ragwort forms a significant part of their diet.
Furthermore, English Nature identify a further 117 species that use ragwort as a nectar source whilst travelling between feeding and breeding sites, or between metapopulations. These consist mainly of solitary bees, hoverflies, moths, and butterflies such as the small copper butterfly (Lycaena phlaeas). Pollen is collected by solitary bees.
Besides the fact that ragwort is very attractive to such a vast array of insects, some of these are very rare indeed. Of the 30 species that specifically feed on ragwort alone, seven are officially deemed Nationally Scarce. A further three species are on the IUCN Red List. In short, ragwort is an exclusive food source for ten rare or threatened insect species, including the Picture Winged Fly (Campiglossa malaris), the Scarce Clouded Knot Horn moth (Homoeosoma nimbella), and the Sussex Emerald moth (Thalera fimbrialis). The Sussex Emerald has been labelled a Priority Species in the United Kingdom Biodiversity Action Plan. A Priority Species is one which is scarce, threatened and declining The remainder of the ten threatened species include three species of Leaf Beetle, another Picture-Winged Fly, and three micro moths. All of these species are Nationally Scarce B, with one Leaf Beetle categorised as Nationally Scarce A.
Without doubt the most common of those species that are totally reliant on ragwort for their survival is the cinnabar moth. The cinnabar is a United Kingdom Biodiversity Action Plan Species, its status described as common and widespread, but rapidly declining. This gives yet more evidence of ragwort's important role in maintaining the country's biodiversity and a vitally important component of the native flora.
Ragwort contains many different alkaloids, making it poisonous to certain animals. (EHC 80,section 9.1.4). Alkaloids which have been found in the plant confirmed by the WHO report EHC 80 are -- jacobine, jaconine, jacozine, otosenine, retrorsine, seneciphylline, senecionine, and senkirkine (pp322 Appendix II). Other alkaloids claimed to be present but from an undeclared source are acetylerucifoline, (Z)-erucifoline, (E)-erucifoline, 21-hydroxyintegerrimine, integerrimine, jacoline, riddelline, senecivernine, spartioidine, and usaramine.
Ragwort is of concern to people who keep horses and cattle. In areas of the world where ragwort is a native plant, such as Britain and continental Europe, documented cases of proven poisoning are rare. Horses do not normally eat fresh ragwort due to its bitter taste. It loses this taste when dried and can become a danger in hay. The result, if sufficient quantity is consumed, can be irreversible cirrhosis of the liver of a form identified as megalocytosis where cells are abnormally enlarged. Signs that a horse has been poisoned include yellow mucus membranes, depression, and lack of coordination. Animals may also resort to the consumption of ragwort when there is shortage of food. Sheep and goats suffer the same process of liver destruction but this is at a reduced rate compared to that in horses and pigs.
There is no definitive test for the poisoning however, since megalocytosis is not a change in the liver which is specific to ragwort poisoning. It is also seen in poisoning by other alkylating agents, such as nitrosamines and aflatoxins. Aflatoxins are a common contaminant formed in feedstuffs by moulds. Research in the United Kingdom has produced results showing megalocytosis, which may be due to various causes, to be a relatively uncommon cause of liver disease in horses.
The danger of ragwort is that the toxin can have a cumulative effect. The alkaloid does not actually accumulate in the liver but a breakdown product can damage DNA and progressively kills cells. About 3-7% of the body weight is sometimes claimed as deadly for horses, but an example in the scientific literature exists of a horse surviving being fed over 20% of its body weight. The effect of low doses is lessened by the destruction of the original alkaloids by the action of bacteria in the digestive tract before they reach the bloodstream. There is no known antidote or cure to poisoning, but examples are known from the scientific literature of horses making a full recovery once consumption has been stopped.
Ragwort poses little risk to the livers of humans since, although it is theoretically poisonous to humans, it is distasteful and is not used as a food. The alkaloids can be absorbed in small quantities through the skin but studies have shown that the absorption is very much less than by ingestion. Also they are in the N-oxide form which only becomes toxic after conversion inside the digestive tract and they will be excreted harmlessly.
Some sensitive individuals can suffer from an allergic reaction because ragwort like many members of the compositae family contains sesquiterpine lactones which can cause compositae dermatitis. These are different from the pyrrolizidine alkaloids which are responsible for the toxic effects.
Honey collected from ragwort has been found to contain small quantities of jacoline, jacobine, jacozine, senecionine, and seneciphylline, but the quantities have been judged as too minute to be of concern.
In the Republic of Ireland, the Noxious Weeds (Thistle, Ragwort, and Dock) Order 1937, issued under the Noxious Weeds Act 1936, declares ragwort as a noxious weed, requiring landowners to control its growth.
In the United Kingdom, common ragwort (Senecio jacobaea) is one of the five plants named as an injurious weed under the provisions of the Weeds Act 1959. The word injurious in this context indicates that it could be harmful to agriculture not that it is dangerous to animals, as all the other injurious weeds listed are non-toxic. Under the terms of this Act, a land occupier can be required by the Secretary of State for Environment, Food and Rural Affairs to prevent the spread of the plant. However, the growth of the plant is not made illegal by the Act and there is no statutory obligation for control placed upon landowners in general.
The Ragwort Control Act 2003 provides for a code of practice on ragwort but does not place any further legal responsibilities on landowners to control the plant.
In ancient Greece and Rome a supposed aphrodisiac was made from the plant; it was called satyrion.
Also, the leaves can be used to obtain good green dye, as yellow dye is obtained from the flowers, as can be done for brown and orange.
The Greek physician Pedanius Dioscorides (c.40-90 CE) recommended the herb. The two "fathers" of herbalism, Gerard and Culpeper, also recommended the herb. Culpeper was an astrological botanist and thought the plant was "under the command of Dame Venus, and [it] cleanses, digests, and discusses."
The poet John Clare had a more positive opinion of the plant, as revealed in this poem of 1831:
Ragwort thou humble flower with tattered leaves
I love to see thee come and litter gold...
Thy waste of shining blossoms richly shields
The sun tanned sward in splendid hues that burn
So bright and glaring that the very light
Of the rich sunshine doth to paleness turn
And seems but very shadows in thy sight.
The ragwort, under its Manx name Cushag, is the national flower of the Isle of Man According to one story King Orry chose as his emblem the cushag flower, as its twelve petals represent one of the isles of the Kingdom of Mann and the Isles: the Isle of Man, Arran, Bute, Islay, Jura, Mull, Iona, Eigg, Rum, Skye, Raasay, and the Outer Hebrides. The ragwort, in fact, usually has thirteen petals. The Manx poet Josephine Kermode (1852–1937) wrote the following poem about the Cushag:
Now, the Cushag, we know,
Must never grow,
Where the farmer's work is done.
But along the rills,
In the heart of the hills,
The Cushag may shine like the sun.
Where the golden flowers,
Have fairy powers,
To gladden our hearts with their grace.
And in Vannin Veg Veen,
In the valleys green,
The Cushags have still a place.
(Vannin Veg Veen is Manx for dear little Isle of Man)
Donald Macalastair of Druim-a-ghinnir on the Isle of Arran told a story of the fairies journeying to Ireland. The ragwort was their transport and every one of them picked a plant, sat astride and arrived in Ireland in an instant.
Ragwort is not cultivated. There are no known varieties.