# Cluster root

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{{Short description|Root structures that aid phosphorus uptake}}
thumb|right|Proteoid roots of ''Leucospermum cordifolium''
'''Cluster roots''', also known as '''proteoid roots''', are [plant](/source/plant) [root](/source/root)s that form clusters of closely spaced short lateral rootlets. They may form a two- to five-centimetre-thick mat just beneath the [leaf litter](/source/leaf_litter). They enhance nutrient uptake, possibly by chemically modifying the soil environment to improve nutrient solubilisation.<ref name="Grierson 1989">{{cite journal | author = Grierson, P.F. and P. M. Attiwill | year = 1989 | title = Chemical characteristics of the proteoid root mat of Banksia integrifolia L. <nowiki>[</nowiki>sic<nowiki>]</nowiki> | journal = [Australian Journal of Botany](/source/Australian_Journal_of_Botany) | volume = 37 | issue = 2 | pages = 137–143 | doi = 10.1071/BT9890137 | bibcode = 1989AuJB...37..137G }}</ref> As a result, plants with proteoid roots can grow in soil that is very low in nutrients, such as the [phosphorus](/source/phosphorus)-deficient native soils of [Australia](/source/Australia).

They were first described by [Adolf Engler](/source/Adolf_Engler) in 1894, after he discovered them on plants of the family [Proteaceae](/source/Proteaceae) growing in [Leipzig Botanic Gardens](/source/Leipzig_Botanic_Gardens). In 1960, Helen Purnell examined 44 species from ten Proteaceae [genera](/source/genus), finding proteoid roots in every genus except ''[Persoonia](/source/Persoonia)''; she then coined the name "proteoid roots" in reference to the plant family in which it was known to occur.<ref name="Purnell 1960">{{cite journal | author = Purnell, Helen M. | year = 1960 | title = Studies of the family Proteaceae: I. Anatomy and morphology of the roots of some Victorian species | journal = [Australian Journal of Botany](/source/Australian_Journal_of_Botany) | volume = 8 | issue = 1 | pages = 38–50 | doi = 10.1071/BT9600038| bibcode = 1960AuJB....8...38P }}</ref> Proteoid roots are now known to occur in 27 different Proteaceae genera, plus around 30 species from other families, including [Betulaceae](/source/Betulaceae), [Casuarinaceae](/source/Casuarinaceae), [Eleagnaceae](/source/Eleagnaceae), [Leguminosae](/source/Leguminosae), [Moraceae](/source/Moraceae) and [Myricaceae](/source/Myricaceae). Similar structures also occur in species of [Cyperaceae](/source/Cyperaceae) and [Restionaceae](/source/Restionaceae), but their [physiology](/source/physiology) is yet to be studied.<ref name="Watt 1999">{{cite journal | author = Watt, Michelle and John R. Evans | year = 1999 | title = Proteoid roots. Physiology and development | journal = [Plant Physiology](/source/Plant_Physiology_(journal)) | volume = 121 | pages = 317–323 | url = http://www.plantphysiol.org/cgi/reprint/121/2/317.pdf | access-date = 2006-11-07 | doi = 10.1104/pp.121.2.317 | issue=2| pmc = 1539228 | pmid=10517822}}</ref>

Two forms are recognised: ''simple'' cluster roots form rootlets only along a root; ''compound'' cluster roots form the primary rootlets, and also form secondary rootlets on the primary rootlets.

Some Proteaceae, such as ''[Banksia](/source/Banksia)'' and ''[Grevillea](/source/Grevillea)'', are valued by the [horticulture](/source/horticulture) and [floriculture](/source/floriculture) industries. In cultivation, only slow-release low-phosphorus [fertilizer](/source/fertilizer)s should be used, as higher levels cause phosphorus toxicity and sometimes [iron](/source/iron) deficiency, leading to plant death. Crop management should minimise root disturbance, and weed control should be via slashing or contact herbicides.

Many plants with proteoid roots have economic value. Cultivated crops with proteoid roots include ''[Lupinus](/source/Lupinus)''<ref name="Hocking and Jeffery 2004">{{cite journal | author = P.J. Hocking and S. Jeffery | year = 2004 | title = Cluster-root production and organic anion exudation in a group of old-world lupins and a new-world lupin | journal = [Plant and Soil](/source/Plant_and_Soil) | volume = 258 | issue = 1 | pages = 135–150 | doi = 10.1023/B:PLSO.0000016544.18563.86 | bibcode = 2004PlSoi.258..135H | s2cid = 25635666 }}<!--| accessdate = 2008-07-18 --></ref> and ''[Macadamia](/source/Macadamia)''.

==References==
{{reflist}}

5. Lambers, H. & Poot, P. (eds) 2003. Structure and Functioning of Cluster Roots and Plant Responses to Phosphate Deficiency.  Kluwer Academic Publishers, Dordrecht.

6. Shane, M.W. & Lambers, H. 2005. Cluster roots: A curiosity in context.  Plant Soil 274: 99–123.  https://doi.org/10.1007%2Fs11104-004-2725-7

7. Lambers, H., Shane, M.W., Cramer, M.D., Pearse, S.J., & Veneklaas, E.J. 2006. Root structure and functioning for efficient acquisition of phosphorus: matching morphological and physiological traits. Ann. Bot. 98: 693–713. http://aob.oxfordjournals.org/cgi/content/abstract/98/4/693

Category:Plant nutrition
Category:Plant anatomy
Category:Plant roots

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Adapted from the Wikipedia article [Cluster root](https://en.wikipedia.org/wiki/Cluster_root) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Cluster_root?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.