Stems are the most basic organs on plants. Simple examples of a stem are twigs, branches, and the trunk(s) of a tree. Stems can range from hard & woody to soft & green (herbaceous), but almost all stems serve a supportive function on a plant. Most people know what a stem looks like, but some plants make the distinction difficult. Some plants have small stems, or underground stems (rhizomes), or leaf-like stems, or stemlike leaves or sometimes lack stems altogether. Although we make neat and clear categories called stems, leaves, and roots, this distinction can be blurred. Grasses are a good example in which the difference between leaf and stem is not easily observable.