Here were three very red poison-oak leaves floating in front of a very deep green background.

A typical tangle of western poison-oak found alongside many wild trails in California. Absent trees to climb, it remains a tangled bush in form. Although most feared because of its red leaves, the green ones are equally irritating.

Up close, the leaf can be seen to resemble the leaf of an oak tree. Despite the resemblance, the poison-oak is not an oak at all, it just has similar leaves. That is why poison-oak is hyphenated, to distinguish it from poison oak.

When a tree is present the poison-oak can climb just like ivy, but it is not an ivy.

Here is a bush of poison-oak growing near or around the trunk of a tree. Just as if it were ivy, some of the stems have already begun to climb the tree.