1 Defining Halophytes: a Conceptual and Historical Approach in an Ecological Frame Marius-Nicuşor Grigore* Alexandru Ioan Cuza University, Iaşi, Romania Abstract Halophytes have certainly been recognized since the beginning of the 18th century, but subtle earlier allusions to salt-tolerant plants can be found back to 1500. By the time of the French Encyclopédie (1751–1765), and Goethe (1786), consistent data about halophytes had already been accumulated. Halophytes were brought to scientific attention through the classic and iconic papers of the German botanist Schimper, and especially those of the Danish plant ecologist Warming. However, their definitions remain controversial; the lack of a unique def- inition is related mainly to the complex features of this ecological group of plants. There are many definitions of halophytes, and some reflect the scientific background of the researchers who defined them. The ‘historical’ evo- lution of a definition can be delineated, and it especially reflects the progress of accumulating knowledge about halophyte biology. The definition of halophytes is thus manifold. The criteria and the historical context in which their definitions occurred and developed are discussed in detail in this chapter. Special attention is given to textual analysis that reveals the convergent approaches of researchers who used different languages. Ecological perspec- tives in defining halophytes suggest that, although they in fact represent a large ecological group of plants, their common xeromorphic nature must be universally recognized. Keywords: Ecology; Halophytes; Saline environments; Xerophytes 1.1 Historical and Semantic frame, with emphasis on the historical and lin- Evolution of Terms guistic evolution of basic terms. It is well known that the history of botany Many definitions of halophytes now exist. Halo- is a part of the history of science and reflects the phytes are so diverse from taxonomical and eco- cultural evolution of humanity (Von Sachs, logical points of view that there is no consensus 1890; Green, 1914; Arber, 1953; Isley, 1994; on a unique definition of the concept of ‘halo- Stevens, 1994; Grigore, 2016; Hardy and Tote- phyte’ (Grigore, 2008, 2012; Grigore et al., lin, 2016). Table 1.2 shows a list of terms, ex- 2010; Grigore and Toma, 2017). Several studies tracted from the languages most used in relation deal with this issue (Grigore et al., 2010, 2014; to halophyte semantics, with special attention Grigore, 2012) and in Table 1.1 new definitions to Latin, which was a rooting language for are mentioned and discussed in a conceptual French and Romanian. Latin was the universal * Corresponding author e-mail: [email protected] © CAB International 2019. Halophytes and Climate Change: Adaptive Mechanisms and Potential Uses (eds M. Hasanuzzaman, S. Shabala and M. Fujita) 3 4 M.-N. Grigore Table 1.1. A review of halophyte definitions (adapted from Grigore et al., 2010, 2014; Grigore, 2012). Definition or descriptions related to halophytes References Comments Plants of the seashore Willdenow First observations of halophytes were made (1805) of plants from seashore – regarded as the ‘absolute’ case of plants growing in saline environments. Later, plants from inland saline habitats were also recognized as halophytes; some botanists referred sometimes to ‘maritime’ and ‘terrestrial’ forms of the same species Plants that vegetate in saline soils Bischoff An ecological definition (1833) Saline plants are those found in maritime Balfour The ‘obligatory’ character of halophytes is situations, or near salt lakes, and which (1862) suggested seem to require much soda in their composition, and which have been called Halophytes Plants which inhabit salt marshes, and by Fowler An ecological definition burning yield barilla (1875) A plant containing a large quantity of Crozier Despite its earlier character, this definition is common salt in its composition, and (1892) interesting because it suggests the which thrives best in salty places capacity of halophytes to accumulate salt in large amounts. We now know that this is a group of halophytes accumulating salts, in contrast to those secreting it Salt-loving plants (are in the most of their Barnes Many plant ecologists consider halophytes characters, strikingly similar to the (1898) a particular case of xerophytes (see xerophytes) further comments in this table) Species of saline and alkaline soils Clements Saline and/or alkaline soils are terms more (salt plants) (1907) precise than other words designating saline environments A certain amount of soluble salts must be Warming How precise is the term ‘certain’? present before halophytic vegetation is called (1909) into existence Plants which grow where the water contains Bower In fact, the soil solution always contains salt; the effect upon them is seen in their (1911) ‘salt’; the issue is concentration. Not all fleshy habit halophytes display a fleshy tissue Strand plants, or Halophytes, living along Ganong We must discriminate that not all halophytes the margin of salt water, and therefore (1913) are strand plants; they can also appear in condensed and otherwise adapted to inland salt marshes/areas the difficult absorption thereof Halo-philous/phytes, plants of sea-coasts Willis Here we can notice the introduction of and salt-steppes, where the presence of (1919) ‘physiological drought’ hypothesis salt, by checking absorption, compels a characterizing saline soils. This is reduction of transpiration ‘famous’ for a certain period of plant ecology (see Grigore and Toma, 2010) Plants which at any stage of their life are Stocker The salt concept is an ambiguous one (see subjected to a concentration of salt, which (1928) the discussions above). It is difficult to is more than ‘normal’ glycophytic plants establish if the plants are exposed all the can bear without dying time to salt, at any stage of their life cycle Continued Defining halophytes – A conceptual approach 5 Table 1.1. Continued. Definition or descriptions related to halophytes References Comments Salt plants; Typical halophytes; true Braun- A good definition of obligate halophytes halophytes; absolute halophytes*; the Blanquet obligate halophytes are plants which for (1932) their normal development need certain ions of the alkali metals and halogens, and which, therefore, can exist and bear seed only in soils containing salt Plants that grow in saline soil or in salty McDougall An interesting definition stating that water are called halophytes and they (1941) halophytes are a peculiar case of are strikingly xeric xerophytes (for extensive comments, see Grigore and Toma, 2010) All plants that are capable of growing in Chapman Chapman’s comments: ‘its use [i.e. the an environment where there is more (1942) definition of ‘halophytes’] will not imply that than 0.5 per cent sodium chloride the species is either common or rare in such habitats nor will the term involve the assumption that a plant cannot grow under any other conditions’. Salinity is a very changeable ecological factor: choosing a number for drawing a line between two different plant groups could be hazardous Plants that can tolerate the concentrations Oosting of salts found in saline soils are termed (1948) halophytes Plants tolerant of various mineral salt in Lawrence the soil solution, usually sodium chloride (1951) Plants growing on salinized media Bucur et al. (1957) Plant that grow exclusively on salt soil Dansereau ‘Exclusively’ could also suggest that (1957) Dansereau was thinking only of euhalophytes Plants growing in saline soils Fernald (1950) Salt-tolerant plants Chapman Neither salt nor tolerant are well defined (1960) [..] the extremely saline soils which are Polunin A good definition of euhalophytes; however, inhabited only by specially adapted plants (1960) growing does not necessarily imply plant (halophytes); plants which habitually grow reproducing in very salty soils – halophytes, or at least can grow in such soils (facultative halophytes); Halophytes are plants which can tolerate a considerable degree of salinity Plants of salty or alkaline soils Correl and Johnston (1970) 1. Plants which grow and complete their life Waisel Very difficult to say precisely what ‘high salt cycle in habitats with a high salt content (1972) content’ represents. This remark of Waisel 2. Usually, the term is reserved only for suggests that the term be applied only to plants which appear in salty habitats euhalophytes (‘true halophytes’) constantly and specifically Continued 6 M.-N. Grigore Table 1.1. Continued. Definition or descriptions related to halophytes References Comments Plants that can tolerate sea water, pure Duncan The sea water concentration is not a or diluted (1974) universal standard, so ‘pure’ or ‘diluted’ could be regarded as relative terms Plants of salty environments; plants adapted Flowers This is perhaps among the first to live in a saline environment, be it et al. physiological definition of halophytes seawater, a salt-water marsh, or a salt- (1986) desert. Plants found growing under naturally saline conditions; for terrestrial plants, this means a minimum salt concentration of about 100 mM in the soil solution. Plants adapted to complete their life cycles in salinities about that of seawater The term halophyte literally means salt Sharma and Perhaps referring also to the character of plants, but is used specifically for plants Gupta euhalophytes that can grow in the presence of high (1986) concentrations of Na salts Those species for which salt marsh