Shrub
A broom shrub in flower stands as a visual anchor for the botanical definition of this plant form. Unlike herbaceous plants, shrubs possess persistent woody stems above ground that survive year after year. Ancient Greek philosopher Theophrastus divided the plant world into trees, shrubs and herbs over two thousand years ago. Most definitions characterize shrubs as possessing multiple stems with no main trunk below ground level. These stems have branched below ground level to create a distinct structural identity. Small shrubs less than one meter tall are sometimes termed subshrubs. Many trees do not reach their mature height because of hostile growing conditions. Some species only last about five years in good conditions while others live beyond 70 years. On average they die after eight years.
Ecologists and evolutionary biologists have paid little attention to why there are two major growth forms of woody plants. One model is based on the advantages of having many stems with larger total stem area for photosynthesis. This structure provides larger area of cambium and phloem compared to a small tree with same initial woody volume. Other advantages include extra stems in case one dies and faster seed production. It is not surprising that at least angiosperm trees revert to shrub growth form when cut or broken. They gain capacity of sprouting at the base thus becoming shrub-like for some time. Many shrubs such as Salix species have good dispersal ability through air-borne seeds. Many shrubs are also able to grow in more extreme habitats like alpine areas where trees are less common.
Shrubland is the natural landscape dominated by various shrubs found across the globe. There are many distinct types around the world including fynbos maquis shrub-steppe shrub swamp and moorland. The last decades have seen shrubification in the arctic with marked increase of shrublands. One reason is increased temperature with consequences for plant community structure and carbon balance. For shrubs that are one to three meters high structural forms are categorized by foliage cover density. Dense foliage cover ranges from 70 to 100 percent creating closed-shrubs. Mid-dense foliage cover spans 30 to 70 percent forming open-shrubs. Sparse foliage cover measures between 10 to 30 percent defining tall shrubland. Very sparse foliage cover under 10 percent creates tall open shrubland environments.
An area of cultivated shrubs in a park or garden is known as a shrubbery. When clipped as topiary suitable species develop dense foliage and many small leafy branches growing close together. Many shrubs respond well to renewal pruning which removes everything but vital parts resulting in long new stems called canes. Other shrubs respond better to selective pruning to dead or unhealthy parts to reveal their structure and character. Shrubs in common garden practice are generally considered broad-leaved plants though some smaller conifers are also shrubby. Species that grow into a shrubby habit may be either deciduous or evergreen. Chris Paul published The Best Evergreen Shrubs for Front Yards on the website Shrubs Radar in 2024. Many garden cultivars exist bred for flowering like rhododendrons and sometimes even leaf colour or shape.
Apart from several berry-bearing shrub species few are eaten directly using culinary rather than botanical definition. They are generally too small for much timber use unlike trees. Those that are used include several perfumed species such as lavender and rose. A wide range of plants with medicinal uses exists within this category. Tea and coffee are on the tree-shrub boundary normally harvested from shrub-sized plants. These would become large enough to become small trees if left to grow instead. Some shrubs produce valuable compounds including Jojoba oil from Simmondsia chinensis. Others provide spices like cinnamon from Cinnamomum species though these often reach tree size. The list includes over one hundred genera ranging from Abelia to Ziziphus with varying commercial applications.
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Common questions
What is the botanical definition of a shrub?
A shrub is defined as a small to medium-sized perennial woody plant with persistent stems above ground that survive year after year. Unlike trees, most shrubs possess multiple stems with no main trunk below ground level.
How long do shrubs live compared to other plants?
Some shrub species last about five years in good conditions while others live beyond 70 years. On average they die after eight years.
Where are shrublands found and what types exist globally?
Shrubland is the natural landscape dominated by various shrubs found across the globe including fynbos maquis shrub-steppe shrub swamp and moorland. The last decades have seen shrubification in the arctic with marked increase of shrublands due to increased temperature.
What is the difference between closed-shrubs and open-shrubs?
Dense foliage cover ranges from 70 to 100 percent creating closed-shrubs while mid-dense foliage cover spans 30 to 70 percent forming open-shrubs. Sparse foliage cover measures between 10 to 30 percent defining tall shrubland environments.
Which shrubs produce valuable compounds or spices for commercial use?
Some shrubs produce valuable compounds including Jojoba oil from Simmondsia chinensis and spices like cinnamon from Cinnamomum species. The list includes over one hundred genera ranging from Abelia to Ziziphus with varying commercial applications.