{{Short description|Salt-tolerant plant}} {{see also|biosalinity|halophile}} {{More citations needed|date=January 2008}} [[Image:Spartina alterniflora.jpg|thumb|250px|right|''Spartina alterniflora'' (cordgrass), a halophyte.]]
A '''halophyte''' is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. The word derives from Ancient Greek ἅλας (halas) 'salt' and φυτόν (phyton) 'plant'.{{source needed|reason=Why ἅλας, gen. ἅλατος instead of ἅλς, gen. ἁλός. The latter seems more probable. Please use a reliable source.|date=March 2025}} Halophytes have different anatomy, physiology and biochemistry than glycophytes.<ref name=":3">Physiology of halophytes, T. J. FLOWERS, Plant and Soil 89, 41–56 (1985)</ref> An example of a halophyte is the salt marsh grass ''Spartina alterniflora'' (smooth cordgrass). Relatively few plant species are halophytes—perhaps only 2% of all plant species.
The large majority of plant species are '''glycophytes''', which are not salt-tolerant and are damaged fairly easily by high salinity.<ref name="Glenn99">{{cite journal | last1 = Glenn | first1 = E. P. | display-authors = etal | year = 1999 | title = Salt tolerance and crop potential of halophytes | journal = Critical Reviews in Plant Sciences | volume = 18 | issue = 2| pages = 227–55 | doi = 10.1080/07352689991309207 | bibcode = 1999CRvPS..18..227G }}</ref>
==Classification== Halophytes can be classified in many ways. According to '''Stocker''' (1933), it is mainly of 3 kinds by habitat, viz.
# '''Aqua-halines''' (aquatic plants) #*''Emerged Halophytes'' (most of the stem remains above the water level) #*''Hydro-halophytes'' (whole or almost whole plant remains under water) # '''Terrestro-halines''' (terrestrial plants) #*''Hygro-halophytes'' (grow on swamp lands) #*''Mesohalophytes'' (grow on non-swamp, non-dry lands) #*''Xero-halophytes'' (grow on dry or mostly dry lands) # '''Aero-halines''' (epiphytes and aerophytes)
Again, according to '''Iversen''' (1936), these plants are classified with respect to the salinity of the soil on which they grow.<ref name="Halophytes: Classification and Characters of Halophytes">{{cite web | title=Halophytes: Classification and Characters of Halophytes | date=29 January 2015| url=http://www.biologydiscussion.com/plants/halophytes-classification-and-characters-of-halophytes-with-diagram/6932}}</ref>
# '''Oligo-halophytes''' (amount of NaCl in the soil is 0.01 to 0.1%) # '''Meso-halophytes''' (amount of NaCl in the soil is 0.1 to 1%) # '''Euhalophytes''' (amount of NaCl in the soil is >1%)
For comparison, seawater has a salinity of about 3.5%. See water salinity for other reference levels.
== Habitats of halophytes == Major habitats where halophytes flourish include mangrove swamps, sand and cliff shorelines in the tropics, salt deserts and semi-deserts, the Sargasso Sea, mudflats and salt marshes, kelp forests and beds, salt lakes and salt steppes of the Pannonian region, wash fringes, isolated inland saline grasslands, and in places where people have brought about salination.<ref name="Kapler2019">Kapler, Adam. 2019. Habitats of Halophytes. In: Halophytes & Climate Change: Adaptive Mechanisms and Potential Uses. Edited by Mirza Hassanuzzaman, Sergey Shabala, & Masayuki Fujita. CAB International. Pp. 19–37.</ref>
== Salt tolerance == True halophytes do not just tolerate saline water, but show optimal growth in saline water.<ref>{{cite journal |last1=Yuan |first1=Fang |last2=Xu |first2=Yanyu |last3=Leng |first3=Bingying |last4=Wang |first4=Baoshan |title=Beneficial Effects of Salt on Halophyte Growth: Morphology, Cells, and Genes |journal=Open Life Sciences |date=2019 |volume=14 |pages=191–200 |doi=10.1515/biol-2019-0021|pmid=33817151 |pmc=7874760 }}</ref>
One quantitative measure of salt tolerance (halotolerance) is the total dissolved solids in irrigation water that a plant can tolerate. Seawater typically contains 40 grams per litre (g/L) of dissolved salts (mostly sodium chloride). Beans and rice can tolerate about 1–3 g/L, and are considered glycophytes (as are most crop plants). At the other extreme, ''Salicornia bigelovii'' (dwarf glasswort) grows well at 70 g/L of dissolved solids, and is a promising halophyte for use as a crop.<ref name=":4"> Glenn, E. P.; Brown, J. J.; O'Leary, J. W. (1998). [http://www.miracosta.edu/home/kmeldahl/writing/..%5Carticles/crops.pdf "Irrigating Crops with Seawater"], ''[http://www.sciam.com Scientific American]'', Vol. 279, no. 8, Aug. 1998, pp. 56–61.</ref> Plants such as barley (''Hordeum vulgare'') and the date palm (''Phoenix dactylifera'') can tolerate about 5 g/L, and can be considered as marginal halophytes.<ref name="Glenn99" />
Adaptation to saline environments by halophytes may take the form of salt tolerance or salt avoidance. Plants that avoid the effects of high salt even though they live in a saline environment may be referred to as facultative halophytes rather than 'true', or obligatory, halophytes.[[File:Pneumatophore overkill - grey mangrove.JPG|thumb|320px|right|Pneumatophores of Grey mangrove]]
For example, a short-lived plant species that completes its reproductive life cycle during periods (such as a rainy season) when the salt concentration is low would be avoiding salt rather than tolerating it. Or a plant species may maintain a 'normal' internal salt concentration by excreting excess salts through its leaves, by way of salt glands, or by concentrating salts in salt bladders in leaves that later die and drop off.<ref name=":3" />
In an effort to improve agricultural production in regions where crops are exposed to salinity, research is focused on improving understanding of the various mechanisms whereby plants respond to salinity stress, so that more robust crop halophytes may be developed. Adaptive responses to salinity stress have been identified at molecular, cellular, metabolic, and physiological levels.<ref name=Gupta-2014>{{cite journal| title=Mechanism of Salinity Tolerance in Plants: Physiological, Biochemical, and Molecular Characterization| first1=Bhaskar| last1=Gupta| first2=Bingru| last2=Huang| journal=International Journal of Genomics| volume=2014| article-number=701596| doi=10.1155/2014/701596| pmid=24804192| date=3 April 2014| pmc=3996477| doi-access=free}}</ref>
==Examples== Some halophytes are: {|class=wikitable ! Taxon ! Common name(s) ! Habitat type ! Tolerance type |- |''Anemopsis californica'' || ''yerba mansa'', lizard tail || Hygro || |- |''Atriplex'' || saltbush, orache, orach || Xero || |- |''Attalea speciosa'' || babassu || Meso || |- |''Dunaliella'' || (a green alga) || Hydro || Eu (seawater) |- |''Halimione portulacoides'' || sea purslane || Hygro || Eu (seawater) |- |''Panicum virgatum'' || switchgrass || Meso, Xero || |- |''Salicornia bigelovii'' || dwarf glasswort, pickleweed || Hygro || Eu (seawater) |- |''Salicornia fruticosa'' || saltworts || ? |- |''Sesuvium portulacastrum'' || sea purslane, shoreline purslane || Hygro || Eu (seawater) |- |''Sporobolus alterniflorus'' || smooth cordgrass || Emerged, Hygro || Eu (seawater) |- |''Suaeda'' || Seep-weeds || Hygro || Eu (seawater) |- |''Tetragonia tetragonioides'' || warrigal greens, ''kōkihi'', sea spinach || Hygro || Eu (seawater) |}
== Uses == ===Biofuel=== {{Main|Biofuel}}
Some halophytes are being studied for use as "3rd-generation" biofuel precursors. Halophytes such as ''Salicornia bigelovii'' can be grown in harsh environments and typically do not compete with food crops for resources, making them promising sources of biodiesel or bioalcohol.<ref name=":4" /><ref>{{cite web |date=December 2013 |title=Fact Sheet: Alternative Fuels |url=https://www.iata.org/pressroom/facts_figures/fact_sheets/pages/alt-fuels.aspx |archive-url=https://web.archive.org/web/20140201191340/https://www.iata.org/pressroom/facts_figures/fact_sheets/pages/alt-fuels.aspx |archive-date=2014-02-01 |access-date=2014-01-28 |publisher=IATA}}</ref><ref>{{Citation |last1=Bresdin |first1=Cylphine |title=Comparison of Seed Production and Agronomic Traits of 20 Wild Accessions of Salicornia bigelovii Torr. Grown Under Greenhouse Conditions |date=2016 |url=https://linkinghub.elsevier.com/retrieve/pii/B9780128018545000054 |work=Halophytes for Food Security in Dry Lands |pages=67–82 |publisher=Elsevier |language=en |doi=10.1016/b978-0-12-801854-5.00005-4 |isbn=978-0-12-801854-5 |access-date=2022-03-05 |last2=Glenn |first2=Edward P. |last3=Brown |first3=J. Jed|url-access=subscription }}</ref>
=== Phytoremediation === Halophytes like ''Suaeda salsa'' can store salt ions and rare-earth elements absorbed from soils in their tissues.<ref name=":0">{{Cite journal|last1=Liang|first1=Jiaping|last2=Shi|first2=Wenjuan|date=2021|title=Cotton/halophytes intercropping decreases salt accumulation and improves soil physicochemical properties and crop productivity in saline-alkali soils under mulched drip irrigation: A three-year field experiment|url=https://linkinghub.elsevier.com/retrieve/pii/S0378429020313113|journal=Field Crops Research|language=en|volume=262|article-number=108027|doi=10.1016/j.fcr.2020.108027|bibcode=2021FCrRe.26208027L |s2cid=230576810|url-access=subscription}}</ref> Halophytes can therefore be used in Phytoremediation measures to adjust salinity levels of surrounding soils.<ref name=":1">{{Cite journal|last1=Brito|first1=Pedro|last2=Caetano|first2=Miguel|last3=Martins|first3=Marcelo D.|last4=Caçador|first4=Isabel|date=December 2020|title=Effects of salt marsh plants on mobility and bioavailability of REE in estuarine sediments|url=https://linkinghub.elsevier.com/retrieve/pii/S0048969720378451|journal=Science of the Total Environment|language=en|volume=759|article-number=144314|doi=10.1016/j.scitotenv.2020.144314|pmid=33338692|s2cid=229325441|url-access=subscription}}</ref> These measures aim to allow '''glycophytes''' to survive in previously uninhabitable areas through an environmentally safe, and cost effective process.<ref name=":2">{{Cite journal|last1=Mann|first1=Ellen|last2=Rutter|first2=Allison|last3=Zeeb|first3=Barbara|date=October 2020|title=Evaluating the efficacy of Atriplex spp. in the phytoextraction of road salt (NaCl) from contaminated soil|url=https://linkinghub.elsevier.com/retrieve/pii/S0269749120310459|journal=Environmental Pollution|language=en|volume=265|issue=Pt B|article-number=114963|doi=10.1016/j.envpol.2020.114963|pmid=32806446|bibcode=2020EPoll.26514963M |s2cid=221162683|url-access=subscription}}</ref> A higher concentration of halophyte plants in one area leads to higher salt uptake and lower soil salinity levels.<ref name=":0" />
Different species of halophytes have different absorption capabilities.<ref name=":1" /> Three different halophyte species (''Atriplex patula, Atriplex hortensis,'' and ''Atriplex canescans)'' have been found to rehabilitate soils contaminated with road salt over varying lengths of time.<ref name=":2" />
== See also ==
* {{annotated link|Biosalinity}} * {{annotated link|Crop tolerance to seawater}} * {{annotated link|Halotolerance}} * {{annotated link|Salt tolerance of crops}} * {{annotated link|Sodium in biology}} * {{annotated link|Soil salinity}} * {{annotated link|Soil salinity control}}
==References== {{reflist}}
== External links == * [https://www.sussex.ac.uk/affiliates/halophytes/ Halophyte database]
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Category:Halophytes Category:Salt marsh plants Category:Aquatic ecology Category:Plant ecology