A woody plant is a plant that uses wood as its structural tissue. These are typically perennial plants whose stems and larger roots are reinforced with wood produced adjacent to the vascular tissues. The main stem, larger branches, and roots of these plants are usually covered by a layer of thickened bark. Woody plants are usually either trees, shrubs, or lianas. Wood is a structural cellular adaptation that allows woody plants to grow from above ground stems year after year, thus making some woody plants the largest and tallest plants.
A plant with true woody stems contains wood, which is primarily composed of structures made of cellulose and lignin. These structures provide support and a vascular system which woody plants use to move water and nutrients from the roots to the leaves and to move sugars from the leaves to the rest of the plant. Most woody plants form new layers of woody tissue each year, and so increase their stem diameter from year to year. New wood is deposited on both sides of a vascular cambium layer that is present near the outer parts of the stem; under the bark on most plants. In some monocotyledons such as palms and dracaenas, the wood is formed in bundles from meristem cells within the trunk.[1] In palms, the wood is formed in the center of the stems. The dermal layer has been modified to protect the stems from the elements with a thickened covering of dead tissue, generally called bark.
Some annual plants appear to form woody stems in their first year, but die at the end of the growing season. They are herbaceous stems without the dead bark covering.
Woody herbs are herbaceous plants that do not have the thickened bark covering, but develop hard stems with vascular bundles. They include such plants as Uraria picta and certain species in family Polygonaceae. These herbs are not truly woody but have hard densely packed stem tissue. Other herbaceous plants have woody stems called a caudex, which is a thickened stem base often found in plants that grow in alpine or dry environments.
Under specific conditions, woody plants may decay or may in time become petrified wood.
The symbol for a woody plant, based on Species Plantarum by Linnaeus is , which is also the astronomical symbol for the planet Saturn.[2]