Red Maple trees, aka. Acer rubrum, are characterized by their showy fall colors of red, yellow, or vivid orange. All parts of the plant are considered poisonous, but leaves (particularly wilted leaves) are the most deadly. Other toxic trees to horses include, but are not limited to: Silver Maple (Acer saccharinum), Sugar Maple (Acer saccharum), and Horsechestnut trees.
Signs of maple toxicity include a darkening of the mucous membranes, feebleness, loss of appetite, lethargy, ataxia (loss of muscular coordination), stomach discomfort, laminitis, dark urine, and in pregnant mares – spontaneous abortion.