Leaves are light to dark green and deeply lobed. The lower leaves form a rosette which die back when flowering is well advanced. The upper part of the stem is highly branched and bears up to 250 bright yellow daisy-like flowers. Single plants are capable of producing over 150,000 seeds, which can remain viable in the soil for years. This weed contains alkaloids that are toxic to cattle, deer, pigs, horses, and goats.
Sheep appear to be less affected, and can consume great quantities without apparent injury.
In susceptible animals, the alkaloids cause degradation of liver function, with lethal results in one to two days when the animal ingests three to seven percent of its body weight in Ragwort. However, such acute poisonings seldom occur because the low palatability of the plant usually results in only small quantities being consumed per day. Chronic effects result from a gradual loss of liver function that eventually develops into a cirrhosis-like condition, eventually leading to death. The alkaloids in Ragwort also rapidly reduce butterfat production in cattle, and taint honey produced by bees such that it is usually too bitter and off-color to market. Although cattle do not generally graze Ragwort directly, the plant's presence in hay often results in the abandonment of the crop.