Halophyte

Halophytes are plants capable of surviving and growing in habitats with high salinity, such as coastal marshes, mangrove swamps, saline deserts, salt marshes, and areas affected by salt spray or salt-rich soils. The term derives from the Greek words halas (salt) and phyton (plant). Only a small fraction of the world’s flora—around two per cent—consists of true halophytes. The remainder are glycophytes, which are not tolerant of high salt levels and are easily damaged by saline conditions.
Halophytes exhibit specialised anatomical, physiological and biochemical characteristics that allow them to flourish under saline stress. A classic example is Spartina alterniflora, or smooth cordgrass, which dominates many salt marsh ecosystems.

Classification

Several systems classify halophytes based on either habitat or the salinity levels of the soils they inhabit.
According to habitat (Stocker, 1933): • Aquahalines – aquatic species.• Emerged halophytes – plants with stems mostly above water level.• Hydrohalophytes – submerged or nearly submerged plants.
Terrestrial groups include: • Hygrohalophytes – species of swampy areas.• Mesohalophytes – plants of moderately moist, non-swamp habitats.• Xerohalophytes – species of dry or semi-dry saline soils.
Aerohalines include epiphytic and aerophytic halophytes found in saline air environments.
According to soil salinity (Iversen, 1936): • Oligohalophytes – tolerate 0.01–0.1 per cent NaCl.• Mesohalophytes – tolerate 0.1–1 per cent NaCl.• Euhalophytes – thrive in soils containing more than 1 per cent NaCl.
For context, seawater has a salinity of about 3.5 per cent.

Habitats

Halophytes occur in a wide range of saline environments worldwide. These include:• mangrove swamps and tidal flats,• salt deserts and semi-deserts,• sand and cliff shorelines,• salt marshes and mudflats,• saline lakes and steppes,• Sargasso Sea and kelp beds,• isolated inland saline grasslands,• landscapes altered by human-induced salinisation.
Their distribution depends on soil salinity, water availability and climatic conditions, producing diverse halophytic communities adapted to local ecological pressures.

Salt Tolerance

True halophytes show optimal growth in saline water, whereas glycophytes generally cannot tolerate more than mild salinity. Salt tolerance can be quantified by the concentration of dissolved solids in irrigation water a species can withstand.
• Most crop plants, including beans and rice, tolerate around 13 g/L.• Barley and the date palm, considered marginal halophytes, tolerate about 5 g/L.• The dwarf glasswort (Salicornia bigelovii) thrives at around 70 g/L and is one of the most salt-tolerant flowering plants known.
Halophytes adapt through either salt tolerance or salt avoidance. Facultative halophytes avoid high salinity by completing their life cycle during low-salinity periods, such as the rainy season. Others maintain internal salt balance by excreting salts through leaf salt glands or storing them in salt bladders that later fall off.

Physiological and Biochemical Adaptations

Halophytes exhibit adaptive responses at the molecular, cellular, metabolic and physiological levels. These include:• ion compartmentalisation and sequestration,• synthesis of osmoprotectants,• specialised epidermal structures for salt excretion,• modified water uptake and retention mechanisms,• robust antioxidant responses to counter salt-induced stress.
Such adaptations make halophytes attractive model organisms for improving salt tolerance in conventional crops.

Economic and Environmental Uses

Halophytes have diverse uses across ecological restoration, agriculture and biotechnology.
Biofuel production: Certain halophytes, particularly Salicornia bigelovii, show potential as third-generation biofuel sources. Their ability to grow in coastal deserts and saline waters reduces competition with food crops and freshwater supplies, making them promising candidates for biodiesel and bioalcohol production.
Phytoremediation: Halophytes absorb salts, trace elements and occasional rare earths from the soil, storing them in roots, stems or leaves. Species such as Suaeda salsa can lower soil salinity and rehabilitate salt-affected soils. Different species vary in their absorption efficiency; Atriplex patula, Atriplex hortensis and Atriplex canescens have been used experimentally to restore sodium chloride-contaminated soils. Higher halophyte density enhances total salt uptake and accelerates soil recovery.

Examples of Halophytes

While there are thousands of species, well-known representatives include:• Spartina alterniflora (smooth cordgrass),• Salicornia bigelovii (dwarf glasswort),• Avicennia marina (grey mangrove),• Atriplex species (saltbushes),• Suaeda species (sea-blite),• Halosarcia and other samphire species,• Limonium species (sea lavenders).
These plants, each with specialised salt-management strategies, play vital ecological roles in stabilising coasts, supporting wildlife, and facilitating nutrient cycling in saline ecosystems.