Fruit are large, angled pods with soft spines. Seeds are a flattened oval with a winged margin and have a terminal tuft of long silky hairs. The sap contains a resin, known as galitoxin, which contributes to its toxicity. Toxic signs are more apparent in animals that cannot vomit, such as horses. They tend to produce a basal rosette of leaves, and later produce alternate leaves along their stems.
Most mustards have yellow flowers with four petals.
Some of the common species in Missouri are wild mustard, field pennycress, tansy mustard, yellow rocket and Virginia pepperweed. Generally, for problems to occur, large quantities have to be consumed over a period of time. Flowers are yellow and occur in clusters at the ends of branches. The fruit is prickly, glossy and leathery brown and has a pale scar. Gastrointestinal signs occur first, with salivation, vomiting, abdominal pain and diarrhea.