Conceptual baseline for a global checklist of gypsophytes

Abstract

The link between plants and gypsum soil dates back to the 19th century. In recent years, an increasing number of articles have dealt with this very special type of flora from various perspectives. The existence of crusts on the soil, xericity and nutritional imbalances that these plants - some of which are mineral accumulators -Are submitted to, have turned them into interesting subjects of study at different levels, from the molecular to the biogeographical and macroecological ones. These plants might represent a relevant model for research on vegetal evolution and specialization, due to the high number of endemisms that concentrate on gypsum, some of them very local and seriously endangered in many cases. As a matter of fact, the Habitats Directive in the E.U. does not only include several gypsophile species, but it also considers gypsum outcrops priority habitats. The creation of a global gypsophytes checklist may favour the possibility to increase knowledge about this interesting flora further. Nevertheless, as there are many gypsum territories in the world, the elaboration of such a list demands the participation of an ever growing number of researchers and local experts. Four aspects have been deemed of interest in this research for the creation of a checklist: Firstly, discussion about whether to consider "gypsum-Tolerant plant" and "gypsophyte" (gypso- from the Greek, gypsum and -phyte, plant) as synonymous terms or not, as happens with "salt-Tolerant plant" and "halophyte" (or "salt tolerance" and "halophily"). In the second place, there is the terminological question that affects all those words derived from the root gyps- (gypsophile, gypsicolous, gypsovag ...) which should be standardized so as to facilitate scientific communication. The third question is related to the gypsiferous soils, or maybe it would better to call them gypsic horizons as the gypsum contents of these can be critical in order to discriminate between gypsophytes and plants that are not so. The fourth aspect deals with the possibility to use chemical composition or stoichiometry in order to discriminate between gypsophytes and the rest of plants, or at least, to discriminate between the accumulative strategy and other nutritional strategies. Finally, a fifth aspect remains to be discussed, highlighting, at least superficially, which territories (in this case, countries) are those where the putative existence of gypsophile flora is believed to appear. Having examined these questions through the revision of 91 papers resulting from a search on Scopus it is clear that gypsum-Tolerance and gypsophily cannot be accepted as synonyms. In addition, gypsophytes, at least for the time being, cannot be defined in any other way but resorting to the classical or inductive criterion, i.e., plants growing exclusively on gypsum. As regards soils, the level of gypsum gypsophile vegetation can tolerate is frequently over 50%. Apart from that, although the accumulator strategy is common among gypsophytes, especially of Ca and S, this is not a trait that can be generalized, as is not the fact that these minerals should concentrate on leaves. Roots, at least in the case of Ca, can also accumulate large quantities. So far, research on gypsophily has focused on around ten countries, which is noteworthy when compared to the 75 where references or signs of gysophile flora have been found; this makes it even more interesting to elaborate a checklist that could broaden knowledge in this area.