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In his 2006 Twinleaf article, "Garden Weeds in the Age of Jefferson," Peter Hatch mentions that Thomas Jefferson considered poison ivy to be an ornamental plant, possibly because of its dramatic fall color.
Jefferson listed elaborate plans for the grounds at Monticello in his Garden Book and Account Book 1771; under "The Open Ground on the West - a shrubbery" Jefferson included "poison oak" under "trees." We assume this to be a reference to poison ivy (Rhus radicans), perhaps included under trees because it is often found climbing up tree trunks. Jefferson also listed other vines under "trees," including "Honeysuckle" and "Jessamine."