Yes, the old saying "Leaves of three, let it be" refers to both poison ivy and poison oak. When young, poison ivy can show up along the ground just a few inches high. It has three distinct leaflets in clusters of three. Often you can see a reddish cast on the petioles (small stems) where the leaflets come together. Older poison ivy vines will climb trees. Their woody vines can get several inches thick and are covered with woody hairlike ariel roots that anchor the vine to the tree trunk the vine climbs. Poison ivy is especially obvious in the fall; with cold fall weather, the foliage turns a bright firey red.