A woody plant is one that uses wood as part of its structural support. These plants are mostly perennials, which mean that they come back year after year without replanting. Not all of the support stems on a woody plant are made of wood, often only the main stems and large roots are wood, while the others are made of softer tissue.
Six different groups encompass woody plants. They include deciduous trees, deciduous shrubs, evergreen trees, evergreen shrubs, woody vines, and woody ground cover. Most people are familiar with deciduous and evergreen trees and shrubs. Woody vines exist in both flowering and non-flowering varieties, and may die in areas that experience cold winters. Woody ground covers, such as creeping juniper, spread through underground rhizomes, or by a process called layering, where the branches develop roots wherever they touch the ground.
Woody plants encompass a range of popular garden plants, and some more rarely seen varieties. A liana is an example of a woody plant that is most commonly seen in the wild. A liana is a vine that has underground roots and climbs trees, winding its way up the tree toward the sunlight, using the tree as support.
Not all plants that appear to be a woody are. Many annual plants develop a stiff, wood like stem over the course of the growing season. The stems become hard due to the sheer volume of tissue. As the cells multiply, the stem becomes rigid, but is not really wood.
Wood is beneficial for plants, as it allows the plant to grow stronger and taller than softer stemmed shrubs and plants. The wood is composed of two materials: lignin and cellulose, which are rigid and provide the support structure for the woody plant. The woody plant also has a vascular system, much like a human's cardiovascular system, to transport nutrients and water through the plant.
Woody plants get wider and taller each year as they lay down new deposits of woody tissue. On most woody plants, the newest tissue is on the outside layer. When looking at a newly cut tree, the wood toward the center of the trunk is the oldest. Some varieties of woody plants, however, most notably certain palm trees, lay down new woody tissue on the inside of the plant, so that the oldest tissue is on the outside of the tree.