Acer rubrum L.—Red maple
FAMILY: Aceraceae—the Maple Family
The maples are generally well known. Flowers are completely or functionally unisexual, usually 5-merous; petals: small, separate, or lacking; stamens: often 8 (5 to 10); ovary: superior, 2-celled, producing a pair of winged, 1-seeded fruits; trees or shrubs with opposite, simple, or occasionally compound leaves.
PHENOLOGY: Acer rubrum flowers March through May; fruits mature May through June.
DISTRIBUTION: Found in swamps, moist uplands, and on alluvial soil.
PLANT CHARACTERISTICS: Tree to 35 m tall; leaves sharply but shallowly lobed, coarsely double-serrate or with a few minor lobes.
POISONOUS PARTS: The leaves are responsible for livestock poisoning. Apparently only wilted leaves are toxic, with toxicity remaining in the leaves for about a month.
SYMPTOMS: Within 18 to 24 hours after consumption of red maple leaves horses begin to show yellow or brown discoloration of the mucous membranes, especially gums and eyelids, urine becomes dark red to brown, and animals become febrile (102.0-103.5°). About 50% of the horses that consume red maple leaves are affected. As many as 64% of those affected die, usually from methemoglobinemia, a destruction of hemoglobin in the blood.
POISONOUS PRINCIPLES: The toxic agent(s) is unknown.
CONFUSED TAXA: There are 10 common species of maples in eastern United States, Acer rubrum is the only maple with all of the following characteristics: simple leaves; angled, sharp sinuses between the principal leaf lobes; flowers appearing much before the opening of the leaf buds; and glabrous fruit maturing in the spring.
SPECIES OF ANIMALS AFFECTED: Only horses and ponies have been reported to develop toxicosis from eating red maple leaves.
TREATMENT: The best treatment is prevention. Do not graze animals in areas where red maples occur. Do not pile branches or leaves in places where stock can reach them. When removing a red maple tree from an area frequented by horses, do it in the winter when the leaves are absent.