A typical leaf consists of a flat blade and a petiole (stalk), which attaches the blade to the stem. Leaves often vary greatly in shape and size among different species. The simplest shape of leaves is the undivided, oval form. The oval-shaped leaf shown in the left photo, for example, is from a sassafras tree. In contrast, many simple leaves are lobed. Not all sassafras leaves are oval, for example; some are divided into a "mitten shape" or a three-lobed shape (as seen in the bottom photo).