Many toxic plants are unpalatable to horses and are not eaten when alternative forage is available. However, when such plants contaminate prepared or baled feed and forage, herd competition and improved palatability can alter acceptance and thereby cause equine plant poisonings. Dehydropyrrolizidine alkaloid-containing plants; cocklebur; Salvia reflexa; kleingrass, switchgrass, and other saponin-containing grasses; jimson weed, black henbane, and other tropane alkaloid-containing plants; lantana; Cassia spp and other myotoxic plants; castor bean; cyanogenic glycoside-containing plants; thiaminase-containing plants; and hoary alyssum are among those that most commonly poison horses in North America via contaminated feed or forage.