Some plants contain saponins, which are detergents, or soaps, and present another danger for horses. Plants that contain saponins include pokeweed, bouncing bet, corn cockle, and English ivy. Though members of different plant families, they all kill liver cells. When plant toxins damage the liver, photoactive substances derived from chlorophyll build up in the blood. These substances are exposed to the sun only in the white areas, so that's where you'll notice blistering, cracking, or loss of outer layers of the skin.
Japanese yew can stop the heart suddenly.
One or two leaves of oleander, a plant found mainly in California, Arizona, and Florida, can kill a horse. White snakeroot causes scarring in the horse's heart and may decrease performance and cause severe heart failure. Horse owners should learn the list of plants, including many popular ornamentals, that can cause the biggest problems and even death in horses. A few castor beans or one little potted hydrangea can kill a horse. Larkspur, a plant sometimes found as an ornamental in the Midwest, can cause paralysis and respiratory failure.