Examples of woody plants include trees and shrubs. Herbaceous plants include other varieties of plant life such as grasses and flowers. Woody plants have stems with rigid outer structures created by lignin, a substance that adds strength to the stem. They grow both upward and outward, developing a trunk or base that is very different from herbaceous plants, which are much more flexible.
Herbaceous plants are classified as either annuals or perennials. Annuals die in the winter. Perennials live for two years or more, though the stems do not become woody. After dying in the winter, new growth originates from the base of the plant in the spring.
Trees and shrubs are differentiated by the number of stems originating from the base. Trees have one main trunk, while shrubs have several stems branching out from the ground. Pruning techniques may make it difficult to classify trees and shrubs correctly.
Trees bearing seeds that are not enclosed by a fruit are called conifers, or gymnosperms. They do not flower. Instead, they have male and female cones that open for pollination. Pines, firs and spruces are all examples of conifers. These trees usually have evergreen leaves that take the form of needles.