Poison ivy usually has a leaf made of of three shiny, oval, pointed leaflets, while poison oak leaves have lobes, says Dummies.com. The lobes of the poison oak, however, are not as deep as those of many oak trees. One problem with both of these plants is that their appearance can change from season to season or plant to plant, says Missouri Botanical Garden.
For example, the leaves of poison ivy are smooth or toothed, says the Missouri Botanical Garden. The leaves are also dull or shiny. The plant grows as a vine or a shrub. It blooms from May through July, has greenish white flowers and white berries that some birds eat.
Poison oak is present in western North America from hardiness zones 5 to 9, according to the Missouri Botanical Garden. Poison ivy is present from South Canada, throughout the United States and south into Guatemala. It is also present in Japan, China and Taiwan. It thrives in zones 4 to 10.
Poison oak is also a much larger plant than poison ivy, which usually grows to about 1 to 3 feet tall with a 1- to-3-foot spread, says Missouri Botanical Garden. By contrast, poison oak grows to 10 feet tall and has up to a 7-foot spread. As a vine, it grows to 50 feet tall. Poison oak also blooms earlier than poison ivy, with its showier flowers appearing between April and June.