Cluster roots, also known as proteoid roots, are
plant roots that form clusters of closely spaced short lateral rootlets. They may form a two- to five-centimetre-thick mat just beneath the leaf litter. They enhance nutrient uptake, possibly by chemically modifying the soil environment to improve nutrient solubilisation.
As a result, plants with proteoid roots can grow in soil that is very low in nutrients, such as the
phosphorus-deficient native soils of
Australia.
They were first described by
Adolf Engler
Heinrich Gustav Adolf Engler (25 March 1844 – 10 October 1930) was a German botanist. He is notable for his work on plant taxonomy and phytogeography, such as ''Die natürlichen Pflanzenfamilien'' (''The Natural Plant Families''), edited with ...
in 1894, after he discovered them on plants of the family
Proteaceae
The Proteaceae form a family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genera with about 1,660 known species. Together with the Platanaceae and Nelumbonaceae, they make up the order Pro ...
growing in
Leipzig Botanic Gardens. In 1960, Helen Purnell examined 44 species from ten Proteaceae
genera, finding proteoid roots in every genus except ''
Persoonia''; she then coined the name "proteoid roots" in reference to the plant family in which it was known to occur.
Proteoid roots are now known to occur in 27 different Proteaceae genera, plus around 30 species from other families, including
Betulaceae
Betulaceae, the birch family, includes six genera of deciduous nut-bearing trees and shrubs, including the birches, alders, hazels, hornbeams, hazel-hornbeam, and hop-hornbeams numbering a total of 167 species. They are mostly natives of the ...
,
Casuarinaceae
The Casuarinaceae are a family of dicotyledonous flowering plants placed in the order Fagales, consisting of four genera and 91 species of trees and shrubs native to eastern Africa, Australia, Southeast Asia, Malesia, Papuasia, and the ...
,
Eleagnaceae,
,
Moraceae and
Myricaceae
The Myricaceae are a small family of dicotyledonous shrubs and small trees in the order Fagales. There are three genera in the family, although some botanists separate many species from ''Myrica'' into a fourth genus ''Morella''. About 55 spe ...
. Similar structures also occur in species of
Cyperaceae
The Cyperaceae are a family of graminoid (grass-like), monocotyledonous flowering plants known as sedges. The family is large, with some 5,500 known species described in about 90 genera, the largest being the "true sedges" genus '' Carex'' w ...
and
Restionaceae
The Restionaceae, also called restiads and restios, are a family of flowering plants native to the Southern Hemisphere; they vary from a few centimeters to 3 meters in height. Following the APG IV (2016): the family now includes the former famil ...
, but their
physiology is yet to be studied.
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
''Banksia'' is a genus of around 170 species in the plant family Proteaceae. These Australian wildflowers and popular garden plants are easily recognised by their characteristic flower spikes, and fruiting "cones" and heads. ''Banksias'' range i ...
'' and ''
Grevillea
''Grevillea'', commonly known as spider flowers, is a genus of about 360 species of evergreen flowering plants in the family Proteaceae. Plants in the genus ''Grevillea'' are shrubs, rarely trees, with the leaves arranged alternately along the b ...
'', are valued by the
horticulture and
floriculture industries. In cultivation, only slow-release low-phosphorus
fertilizers should be used, as higher levels cause phosphorus toxicity and sometimes
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
''Lupinus'', commonly known as lupin, lupine, or regionally bluebonnet etc., is a genus of plants in the legume family Fabaceae. The genus includes over 199 species, with centers of diversity in North and South America. Smaller centers occur ...
''
and ''
Macadamia
''Macadamia'' is a genus of four species of trees in the flowering plant family Proteaceae. They are indigenous to Australia, native to northeastern New South Wales and central and southeastern Queensland specifically. Two species of the genus ...
''.
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
Plant nutrition
Plant roots