This is a native plant and is a member of the daisy (Aesteracea) family, it is not invasive and likes to set up home on wasteland or churned up patches of soil in fields and hedgerows. There is a lot of controversy surrounding ragwort, particularly its ability to kill horses by causing liver failure. But it is only when it gets mixed up in the hay that it can be accidentally ingested by the animal, otherwise it presents few problem as a horse will rarely eat fresh ragwort, knowing to avoid it.
The plant contains pyrrolizidine alkaloids, the same chemical found in comfrey root, and these alkaloids can be hepatotoxic which is why medical herbalists no longer prescribe comfrey root internally either. These alkaloids do not, however, accumulate in the liver as is often stated, and they are excreted quite quickly. They have to be consumed in large quantities over a period of time to cause progressive damage to the liver.
Ragwort used to be widely used in herbal medicine to lower fever and treat digestive disorders. It is not a herb I use, but I do know it is reputed to reduce inflammation and pain when applied as a poultice and is used in this manner for conditions such as arthritis and sciatica. Importantly it also supports numerous insects including the beautiful Cinnabar moth for which it is the caterpillar’s main food source.