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Oak leaves and acorns are both poisonous, and they're known to cause agitation, liver damage, and abdominal pain. Oak leaves are usually deeply lobed and a dark, rich green color.  Oaks can be found in the Americas, Asia, Europe and part of North Africa. Oak leaves are poisonous to both humans and most animals, and they should never be grown near livestock. Oleander trees are extremely poisonous and often fatal. Ingesting an oleander leaf or branch can cause heart problems, digestive upset, and even death. Oleander leaves can be identified by their long and thin blades, leathery texture, and tendency to grow in pairs or groups of 3. Oleander plants are native to the Mediterranean region but is a common ornamental tree in gardens all over the world. Ohio buckeyes are highly poisonous trees that can cause vomiting, diarrhea, dilated pupils, paralysis, and death. The leaves are arranged in pairs of 5-7, resembling fingers on a hand, and are a bright green color with jagged edges. Buckeyes are the state tree of Ohio, and the plant is native to the midwestern United States. Although chokecherry berries are safe to eat, every other part of the plant (including the berry pit) is poisonous. Chokecherry leaves are wide and flat, with curved veins, a fine-toothed edge, and a petiole less than 1/3 the length of the entire leaf. Chokecherry plants are also poisonous to horses and cattle, causing labored breathing, muscle spasms, and death in extreme cases. Manchineel trees, among the most poisonous plants in the world, ooze a toxic sap that can cause blistering, respiratory problems, or death in humans. Manchineel leaves can be recognized by their long petiole, shiny yellow-green blade, and thinly serrated edges. Manchineel trees are native mainly to the Caribbean and the Gulf of Mexico, though they can also be found in the southern United States.
Recognize oak leaves by their dark green, glossy leaves. Watch out for oleander leaves, which grow in pairs or groups of 3. Note the Ohio buckeyes' broad, bright leaves with jagged edges. Watch for the chokecherry tree's curved veins and short petiole. Spot Manchineel leaves by their shiny, fine-toothed leaves.