The animal will breathe rapidly and deeply, then become anxious and stressed. Progressing symptoms include trembling, incoordination, attempts to urinate and defecate and collapsing. Finally, respiratory or cardiac arrest may occur, leading to a violent death. Most have a thick, milky sap in their leaves, stems and seedpods. 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.