Bur

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Geum bur
Hooked burs of Arctium (Burdock)
Close-up of a single Arctium bur

A bur (also spelled burr)[1] is a seed or dry fruit or infructescence that has hooks or teeth. The main function of the bur is to spread the seeds of the bur plant, often through epizoochory. The hooks of the bur are used to catch on to for example fur or fabric, so that the bur, which contain seeds, then can be transported along with the thing it attached itself to.[2] Another use for the spines and hooks are physical protection against herbivores.[3] Their ability to stick to animals and fabrics has shaped their reputation as bothersome.

Some other forms of diaspores, such as the stems of certain species of cactus also are covered with thorns and may function as burs.

Bur-bearing plants such as Xanthium species are often single-stemmed when growing in dense groups, but branch and spread when growing singly.[4] The number of burs per fruit along with the size and shape can vary largely between different bur plants.[5]

Function[edit]

Containing seeds, burs spread through catching on the fur of passing animals (epizoochory) or machinery as well as by being transported together with water, gravel and grain.[2] The hooks or teeth generally cause irritation, and some species commonly cause gross injury to animals, or expensive damage to clothing or to vehicle tires.

Burs serve the plants that bear them in two main ways.

Spinescent plants repel herbivores mechanically by wounding the herbivore's mouth or digestive system. Moreover, burs' mechanical defence can work alongside the color of the bur that can visually warn off herbivores.[3]

Most epizoochorous burs attach to hair on the body or legs of the host animal, but a special class of epizoochorous bur is known as the trample-bur (or trample-burr). Several species of Tribulus, Harpagophytum, and Grielum produce fruit in the form of trample-burs. As the name suggests, they attach themselves to the animal when trampled. They may hook onto the legs of animals as the large hooks of Harpagophytum do, sometimes causing serious injury, but sometimes hooking onto the leg of say, an ostrich, apparently without causing discomfort.[7] It also might penetrate a hoof or foot pad or the tires of a vehicle, only to be shed after being carried for a considerable time and distance; most Tribulus and Grielum species are specialised for such attachment, variously being flat, but with upward-directed spikes as in say, Grielum humifusum,[8] or shaped like a caltrop as in some species of Tribulus that have achieved the status of cosmopolitan weeds by sticking to the tires of aircraft.[9]

The bur must be able to easily detach from the plant and easily attach to for example the fur of an animal. The ability to spread the seeds depends both on the number of burs that manage to get attached and on force of attachment. The hook span of the bur has been shown to have a large influence on the contact separation force. Some studies have also shown force can increase with the size of the birr, although not all large burs have a high contact separation force. Furthermore, the flexibility of the bur might also influence this force which can increase with stiffness. [5]

Relevance to humans[edit]

Burs are best known as sources of irritation, injury to livestock,[2] damage to clothing, punctures to tires, and clogging equipment such as agricultural harvesting machinery. Furthermore, because of their ability to compete with crops over moisture and nutrition, bur plants can be labelled as weeds and therefore also be subject to removal. Methods of controlling the spread of bur plants include the use of herbicides, slashing and cultivation among others.[2]

Some have however been used for such purposes as fabric fulling, for which the fuller's teasel is a traditional resource.

The bur of burdock was the inspiration for hook and loop fastener, also known as Velcro.[10]

Common plants with burs[edit]

Common bur-bearing plants include:

References[edit]

  1. ^ Cook, J. Gordon (1968). ABC of Plant Terms. Watford, Herts: Merrow. OCLC 223208923.
  2. ^ a b c d Johnson, A and Trounce, B (2015). "Californian burr (Xanthium orientale)". weeds.dpi.nsw.gov.au. Archived from the original on 2019-02-28. Retrieved 2021-10-29.{{cite web}}: CS1 maint: multiple names: authors list (link)
  3. ^ a b c Xu, Qi; Lev-Yadun, Simcha; Sun, Lu; Chen, Zhe; Song, Bo; Sun, Hang (2020-04-01). "Spinescent patterns in the flora of Jiaozi Snow Mountain, Southwestern China". Plant Diversity. 42 (2): 83–91. doi:10.1016/j.pld.2019.12.002. ISSN 2468-2659. PMC 7195588. PMID 32373766.
  4. ^ Noogoora burr, Californian burr, Italian cockleburr and South American burr (Xanthium species). New South Wales Department of Primary Industries. 2009.
  5. ^ a b Gorb, Elena; Gorb, Stanislav (2002-04-01). "Contact separation force of the fruit burrs in four plant species adapted to dispersal by mechanical interlocking". Plant Physiology and Biochemistry. 40 (4): 373–381. doi:10.1016/S0981-9428(02)01381-5. ISSN 0981-9428.
  6. ^ a b Magee, M. B. Plants With Burrs. San Francisco Chronicle.
  7. ^ Midgley, J.J. and Illing, N. Were Malagasy Uncarina fruits dispersed by the extinct elephant bird? South African Journal of Science 105, November/December 2009
  8. ^ Karen van Rheede van Oudtshoorn; Margaretha W. van Rooyen (1999). Dispersal Biology of Desert Plants. Springer. pp. 95–. ISBN 978-3-540-64886-4.
  9. ^ Holm, L. et al. A geographical atlas of world weeds. Krieger 1991, ISBN 978-0894643576
  10. ^ Suddath, Claire (15 June 2010). "A Brief History of: Velcro". Time. Retrieved 17 October 2018 – via content.time.com.
  11. ^ "ITIS - Report: Acanthospermum australe". www.itis.gov. Retrieved 2021-11-13.
  12. ^ "Agrimonia pubescens - Michigan Flora". michiganflora.net. Retrieved 2021-11-13.
  13. ^ "Anthriscus caucalis". www.calflora.org. Archived from the original on 2021-03-05. Retrieved 2021-11-13.
  14. ^ "Arctium lappa L. GRIN-Global". npgsweb.ars-grin.gov. Retrieved 2021-11-13.
  15. ^ Cenchrus longispinus. University of California IPM.
  16. ^ "Circaea lutetiana subsp. canadensis (Broadleaf Enchanter's Nightshade) | North Carolina Extension Gardener Plant Toolbox". plants.ces.ncsu.edu. Retrieved 2021-11-13.
  17. ^ "Daucus carota (Bee's Nest-Plant, Bird's-Nest, Devil's Plague, Queen Anne's Lace, Wild Carrot) | North Carolina Extension Gardener Plant Toolbox". plants.ces.ncsu.edu. Retrieved 2021-11-13.
  18. ^ "Hylodesmum glutinosum (Muhlenberg ex Willdenow) H. Ohashi & R.R. Mill - Database of Vascular Plants of Canada (VASCAN)". data.canadensys.net. Retrieved 2021-11-13.
  19. ^ Gorb, E.; Gorb, S. (2002). "Contact separation force of the fruit burrs in four plant species adapted to dispersal by mechanical interlocking". Plant Physiology and Biochemistry. 40 (4): 373–381. doi:10.1016/S0981-9428(02)01381-5.
  20. ^ [1] Ontario Wildflowers
  21. ^ [2] Ontario Wildflowers
  22. ^ "Geum urbanum Linnaeus - Database of Vascular Plants of Canada (VASCAN)". data.canadensys.net. Retrieved 2021-11-13.
  23. ^ "USDA Plants Database". plants.sc.egov.usda.gov. Retrieved 2021-11-13.
  24. ^ "USDA Plants Database". plants.usda.gov. Retrieved 2021-11-13.
  25. ^ Tribulus terrestris. University of California IPM.
  26. ^ Xanthium strumarium. University of California IPM.

External links[edit]