Biology:Shrub

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Short description: Small- to medium-sized perennial wood plant
A broom shrub in flower
A rhododendron shrubbery in Sheringham Park

A shrub or bush is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple stems and shorter height, less than 6–10 m (20–33 ft) tall.[1][2] Small shrubs, less than 2 m (6.6 ft) tall are sometimes termed as subshrubs. Many botanical groups have species that are shrubs, and others that are trees and herbaceous plants instead.

Some define a shrub as less than 6 m (20 ft) and a tree as over 6 m. Others use 10 m (33 ft) as the cutoff point for classification.[2] Many trees do not reach this mature height because of hostile, less than ideal growing conditions, and resemble shrub-sized plants. Others in such species have the potential to grow taller in ideal conditions. For longevity, most shrubs are classified between perennials and trees. Some only last about five years in good conditions. Others, usually larger and more woody, live beyond 70. On average, they die after eight years.[3]

Shrubland is the natural landscape dominated by various shrubs; there are many distinct types around the world, including fynbos, maquis, shrub-steppe, shrub swamp and moorland. In gardens and parks, an area largely dedicated to shrubs (now somewhat less fashionable than a century ago) is called a shrubbery, shrub border or shrub garden. There are many garden cultivars of shrubs, bred for flowering, for example rhododendrons, and sometimes even leaf colour or shape.

Compared to trees and herbaceous plants, perhaps a relatively small number of shrubs have agricultural or commercial uses. Apart from the several berry-bearing species (using the culinary rather than botanical definition), few are eaten directly, and they are generally too small for much timber use unlike trees.[4] Those that are used include several perfumed species such as lavender and rose, and a wide range of plants with medicinal uses. Tea and coffee are on the tree-shrub boundary;[5] they are normally harvested from shrub-sized plants, but these would be large enough to become small trees if left to grow instead.

Definition

Shrubs are perennial woody plants, and therefore have persistent woody stems above ground (compare with succulent stems of herbaceous plants).[2] 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).[2] Ancient Greece philosopher Theophrastus divided the plant world into trees, shrubs and herbs.[6]

Small, low shrubs, generally less than 2 m (6.6 ft) tall, such as lavender, periwinkle and most small garden varieties of rose, are often termed as subshrubs.[7][8]

Most definitions characterize shrubs as possessing multiple stems with no main trunk below.[2] 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 without a reasonable length beforehand. Many trees can grow in multiple stemmed forms also while being tall enough to be trees, such as oak or ash.[2]

Use in gardens and parks

An area of cultivated shrubs in a park or a garden is known as a shrubbery.[9] When clipped as topiary, suitable species or varieties of shrubs develop dense foliage and many small leafy branches growing close together.[10] Many shrubs respond well to renewal pruning, in which hard cutting back to a "stool", removes everything but vital parts of the plant, resulting in long new stems known as "canes".[11] Other shrubs respond better to selective pruning to dead or unhealthy, or otherwise unattractive parts to reveal their structure and character.[12]

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.[13]

Botanical structure

Shrub vegetation (with some cactus) in Webb County, Texas.
Blackthorn shrub (Prunus spinosa) in the Vogelsberg
Hydrangea macrophylla
Winter-flowering Witch-hazel (Hamamelis)
Senecio angulatus, a scrambling shrub by the sea (yellow-flowered).

In botany and ecology, a shrub is more specifically used to describe the particular physical canopy structure or plant life-form of woody plants which are less than 8 metres (26 ft) high and usually multiple stems arising at or near the surface of the ground. 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.[14]

For shrubs that are 2–8 metres (6.6–26.2 ft) high, the following structural forms are categorized:

  • dense foliage cover (70–100%) — closed-shrubs
  • mid-dense foliage cover (30–70%) — open-shrubs
  • sparse foliage cover (10–30%) — tall shrubland
  • very sparse foliage cover (<10%) — tall open shrubland

For shrubs less than 2 metres (6.6 ft) high, the following structural forms are categorized:

  • dense foliage cover (70–100%) — closed-heath or closed low shrubland—(North America)
  • mid-dense foliage cover (30–70%) — open-heath or mid-dense low shrubland—(North America)
  • sparse foliage cover (10–30%) — low shrubland
  • very sparse foliage cover (<10%) — low open shrubland

List

Those marked with * can also develop into tree form if in ideal conditions.

A
B
C
D
E
F
G
H
I
J
K
  • Kalmia (Mountain-laurel)
  • Kerria (Kerria)
  • Kolkwitzia (Beauty-bush)
L
M
N
O
P
Q
R
S
T
U
  • Ulex (Gorse)
  • Ulmus pumila celer (Turkestan elm – Wonder Hedge)
  • Ungnadia (Mexican Buckeye)
V
W
X
Y
Z


References

  1. ↑ Lawrence, Anna; Hawthorne, William (2006). Plant Identification: Creating User-friendly Field Guides for Biodiversity Management. Routledge. pp. 138–. ISBN 978-1-84407-079-4. https://books.google.com/books?id=rHEpVBM5-eIC&pg=PA138. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Allaby, Michael (2019) (in en). A dictionary of plant sciences. Oxford Oxford University Press. ISBN 9780198833338. OCLC 1097073225. 
  3. ↑ "Life Spans of Small Trees and Shrubs" (in en-US). 2014-02-27. https://temeculalandscapeconstruction.com/life-spans-of-small-trees-and-shrubs/. 
  4. ↑ Rosewood does not come from roses.
  5. ↑ Clayton, Liz (20 October 2021). "Is The Coffee Plant A Tree, Bush, Or Shrub?" (in en-US). https://sprudge.com/is-the-coffee-plant-a-tree-bush-or-shrub-181869.html. 
  6. ↑ Bremness, Lesley (1994). The complete book of herbs. Viking Studio Books. p. 8. ISBN 9780140238020. https://books.google.com/books?id=VqfnrH-W2kwC. 
  7. ↑ Fischer, Peggy (1990). Essential shrubs: the 100 best for design and cultivation. Friedman/Fairfax Publishers. pp. 9–. ISBN 978-1-56799-319-6. https://books.google.com/books?id=QuLtawHEsJMC. "... Examples of subshrubs include candytuft, lavender, and rosemary. These broad definitions are ..." 
  8. ↑ "What is a Subshrub?" (in en-US). 2017-05-15. https://worldoffloweringplants.com/subshrub/. 
  9. ↑ Whitefield, Patrick (2002). How to Make a Forest Garden. Permanent Publications. pp. 113–. ISBN 978-1-85623-008-7. https://books.google.com/books?id=3rd3e69BnC8C&pg=PA113. 
  10. ↑ Varkulevicius, Jane (17 May 2010). Pruning for Flowers and Fruit. Csiro Publishing. ISBN 9780643101975. https://books.google.com/books?id=a93TcRVsqLwC&q=topiary+pruning+dense+foliage&pg=PA100. Retrieved 19 December 2017. 
  11. ↑ "Rejuvenation or Renewal Pruning to Restore Overgrown Shrubs" (in en-US). 2019-02-21. https://organicplantcarellc.com/rejuvenation-or-renewal-pruning-to-restore-overgrown-shrubs/. 
  12. ↑ Turpin, Jason (2018-08-29). "What is Selective Tree and Shrub Pruning-How to Prune Correctly!" (in en-US). https://www.turpinlandscapedesign.com/what-is-selective-tree-and-shrub-pruning-landscape-experts-answer-your-questions/. 
  13. ↑ Elliott, Franklin Reuben (1 November 2008). Popular Deciduous and Evergreen Trees and Shrubs. Applewood Books. ISBN 9781429012904. https://books.google.com/books?id=vlDxSBGB0cYC&q=shrub+deciduous+or+evergreen. Retrieved 19 December 2017. 
  14. ↑ Costermans, L. F. (1993) Native trees and shrubs of South-Eastern Australia. rev. ed. ISBN:0-947116-76-1



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