A shrub or bush is a small- to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. They are distinguished from trees by their multiple stems and shorter height, less than 6 m-10 m (20 ft–33 ft) tall. Small shrubs, less than 2 m (6.6 ft) tall are sometimes termed subshrubs.
Shrubs are perennial woody plants, and therefore have persistent woody stems above ground (compare with herbaceous plants). Usually shrubs are distinguished from trees by their height and multiple stems. Some shrubs are deciduous (e.g. hawthorn) and others evergreen (e.g. holly). Ancient Greek philosopher Theophrastus divided the plant world into trees, shrubs and herbs.
Some definitions state that a shrub is less than 6 m and tree is over 6 m. Others use 10 m as the cut off point. Many species of tree may not reach this mature height because of less than ideal growing conditions, and resemble a shrub sized plant. However such species have the potential to grow taller under the ideal growing conditions for that plant.
Most definitions characterize shrubs as possessing multiple stems with no main trunk. This is because the stems have branched below ground level. There are exceptions to this, with some shrubs having main trunks, but these tend to be very short and divide into multiple stems close to ground level. Many trees can grow in multiple stemmed forms also, such as oak or ash.[clarification needed]
An area of cultivated shrubs in a park or a garden is known as a shrubbery. When clipped as topiary, suitable species or varieties of shrubs develop dense foliage and many small leafy branches growing close together. Many shrubs respond well to renewal pruning, in which hard cutting back to a "stool" results in long new stems known as "canes".[clarification needed] Other shrubs respond better to selective pruning to reveal their structure and character.
Shrubs in common garden practice are generally considered broad-leaved plants, though some smaller conifers such as mountain pine and common juniper are also shrubby in structure. Species that grow into a shrubby habit may be either deciduous or evergreen.
In botany and ecology, a shrub is more specifically used to describe the particular physical structural or plant life-form of woody plants which are less than 8 metres (26 ft) high and usually have many stems arising at or near the base.[clarification needed] For example, a descriptive system widely adopted in Australia is based on structural characteristics based on life-form, plus the height and amount of foliage cover of the tallest layer or dominant species.
For shrubs 2–8 metres (6.6–26.2 ft) high the following structural forms are categorized:
For shrubs less than 2 metres (6.6 ft) high the following structural forms are categorized:
Those marked with * can also develop into tree form.
... Examples of subshrubs include candytuft, lavender, and rosemary. These broad definitions are ...