A halophyte is a plant that completes its life cycle in a salty environment; many survive in seawater or even higher concentrations of salt. Most other plants (called glycophytes) cannot survive even one tenth the salt concentration found in seawater; this group includes virtually all our crop plants. Given the extent of salt-affected land, perhaps 6% of the world's land surface and a continued increase in the extent of agricultural land that is salt-affected, knowledge of plants that can tolerate salt provides a basis for the restoration of this land and to understanding the genetics, biochemistry and physiology of salt tolerance in plants as an aid to plant breeding.

HALOPH

A comprehensive list of halophytes was compiled by James Aronson during the 1980s: his 'HALOPH A Data Base of Salt Tolerant Plants of the World' was published in 1989 by the Office of Arid Land Studies at the University of Arizona, Tucson, Arizona. This list of 1560 species for which there is evidence that they are salt tolerant was arranged by family, genus and species and included data on salinity tolerance, together with photosynthetic pathway where known, life form, plant type, economic use and distribution (Aronson, 1989)

The primary criterion for inclusion in HALOPH was “known or presumed tolerance to electrical conductivity measuring (or estimated to be) at least 7.8 dS m-1, during significant periods of the plant’s entire life” (Aronson 1989). Aronson wrote that this salinity tolerance was “the maximum reported salinity tolerance of a taxon as reported in the References Cited. ... However, the reader is reminded that salinity tolerance is very much affected by other factors - season, humidity, drainage, nutrition, and the like. In addition, under field conditions, soil salinity varies significantly across a soil profile. Thus, a considerable number of difficulties arise in interpretation, and particularly, in attempted application of data of such diverse origins. Therefore readers of HALOPH are urged to go to primary sources before drawing final conclusions about a given plant's salt tolerance."

The salinity tolerated was reported in the units (dS/m) most commonly accepted for the estimation of salinity - the electrical conductivity of a saturation extract.

SW was the only non-exact term used for the salinity field by Aronson. It stands for seawater of unknown electrical conductivity (ECi), to which the species is generally exposed for at least part of each day. In such cases, ECi of SW is assumed to be at least 40 dS m1.

eHALOPH

The data in HALOPH is (with permission) the basis of eHALOPH. Over the period 2002 to 2005 the printed database (Aronson 1989) was converted to an electronic format by scanning, use of text recognition software and manual editing. The files generated in Microsoft Excel were incorporated first into an Access database and then into MySQL tables. The current version retains the basic format of HALOPH with data being organised taxonomically by family, genus and species. The taxonomy was initially updated to that in ‘The Plant List’: (http://www.theplantlist.org/) and from November 2018 to that in Plants of the World Online [www.plantsofhteworldonline.org]. Original data on plant type, life form, maximum salinity tolerated, photosynthetic pathway and economic uses have been supplemented with data on optimal salinity for growth, antioxidants, secondary metabolites, compatible solutes and habitat and whether or not there have been publications on ion contents (ionomics), ecotypes, germination, the presence or absence of salt glands molecular data, microbial interactions and mycorrhizal status. The geographical distribution of species provided in HALOPH was only descriptive and this field has been supplemented and enriched in eHALOPH by providing distribution maps from GBIF.

In V4 of eHALOPH the salinity data has been extended to provide the range of values reported in the literature; we have added other units (g/kg, mg/l, %, PSU and mM) to enable us to achieve this. SW has been converted to 35.5 PSU (Practical Salinity Units). A high degree of seasonal and geographical variation is of course involved in seawater salinity levels.
The database has been checked and compared with a list prepared by Menzel and Lieth (2003) and with a list of halophytes found in China (Zhao et al 2002).

The current verion (V5) of eHALOPH has been developed over a three year period, from Version 3 using funding from the Gatsby Foundation, finishing at the end of September 2022. An earlier version of eHALOPH can also be seen in Kew's Seed Information Database (SID) http://data.kew.org/sid/about.html. Data from version 3.09 of eHALOPH is available in theTRY database (https://www.try-db.org/TryWeb/Home.php). More detail of Version 3 can be found in Santos et al (2016). Version 5 ie essentially similar to Version 4, but includes various software and administrative updates.

Aronson, J.A. 1989. HALOPH A Data Base of Salt Tolerant Plants of the World, Office of Arid Land Studies, University of Arizona, Tucson, Arizona, 75 pp].

Menzel, U and Lieth, H. 2003. HALOPHYTE database Vers. 2.0 update. In Cash Crop

Halophytes, edited by Lieth, H. and Mochtchenko, M. Compact Disc. Kluwer, Dordrecht.
Santos J, Al-Azzawi M, Aronson J, Flowers TJ. 2016. eHALOPH a Database of Salt-Tolerant Plants: Helping put Halophytes to Work. Plant & Cell Physiology, 57 (1): e10(1–10) (2016) doi:10.1093/pcp/pcv155.

Zhao K.F., Fan H., Ungar I.A. 2002. Survey of halophyte species in China. Plant Science 163 (3):491-498