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What is a Ragwort?

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  • Written By: Alex Tree
  • Edited By: Melissa Wiley
  • Last Modified Date: 10 November 2016
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Ragworts, native wildflowers in northern Eurasia and the United States, belong to the genera Senecio, Rugelia, and Packera. Depending on the area where the species thrive, they can occur in varied forms such as shrubs, climbers, and aquatics. Different species are widely distributed weeds in open, dry places. The obnoxious smell of the leaves has led to the many malodorous names given to the plant, such as mare’s fart, stinking ninny, and tansy ragwort.

Ragwort plants that resemble small trees are described botanically as annuals or perennials. The straight and erect stems of these groundsels hold bright yellow flower heads in flat-topped clusters that are often dense. Ragwort flowers are hermaphrodites and can be easily pollinated by bees, butterflies, and moths. In the northern hemisphere, the flowering period usually starts in June and ends in November.

Caterpillars and the larvae of moths use the ragwort shrubs as food plants. After absorbing the plants’ alkaloids, these potential prey become repulsive to their predators. In countries like the United States and New Zealand where ragwort has become a problem, moths serve as a means of prevention and control. On the other hand, the plant is a vital part of the native flora in the United Kingdom because its nectar is used as a food source for hundreds of invertebrate species, with at least 30 of these species either being rare or declining in population.

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Compounds in the common ragwort, called pyrrolizidine alkaloids, are toxic to most vertebrates. When inside the plants, the poisonous compound is in a non-toxic form; hence humans can handle it without risk to their health. In order to reach the point of toxicity, the plant needs to be eaten, processed by the intestines, and then broken down by the liver. Contrary to popular belief, these alkaloids do not have the chance to accumulate in an animal’s body because they are excreted as waste within 24 to 48 hours. To reach a lethal dose, a human being has to consume 14 pounds (6 kg) of the plant.

An allergic reaction medically referred to as compositae dermatitis may occur when these plants come in contact with the skin of sensitive individuals. Sesquiterpene lactones, a chemical commonly produced by plant species of the Daisy family, is the main culprit for the allergy. These lactones, however, do not have the ability to cause the long-term liver problems brought about by pyrrolizidine alkaloids.

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