The species is rather distinct. Within the genus Acarospora is one of the few terricolous placoid species. Acarospora nodulosa may be closely related and occurs in similar habitat, however it is easily distinguished by the presence of rhizocarpic acid in A. placodiiformis giving thalli a yellowish tinge, especially observed in young specimens and wet specimens.
The species seems to be a Mediterranean endemic exclusively associated with gypsum soils and dry continental climates. It shows a scattered distribution with records from Spain, Morocco, Italy, Greece, Iran, Germany (doubtful) and Turkey (US records not reliable). Major threats are: a) habitat loss by agricultural uses, trampling, urban pressure, mining and off-road motorcycling, b) low connectivity among populations,
Criterion A. We assume for this species a generation time of 30 years, estimating the time for population reduction record -and application of criterion A- in c. 100 years. There is scarce information about trends or population sizes in most of its distribution, however it seems that it is restricted to single localities in most of the countries. In Spain, where the species was described from, there is a clear and documented trend in the loss of habitat during the last century (Mota et al. 2011). The causes of habitat loss (changes in land use due to a change from grazing steppes to crop fields, gypsum, glauberit and thenardite mining, urban pressure, expansion of the road network) have not stop during the past decades, instead pressure has increased (Mota et al. 2010). Further, repopulation with Pinus pinaster has been the cause of severe losses of natural gypsum steppes during the past decades. Thus, according to subcriteria A2, A3 and A4 (a: direct observation & c: decline in the area of occupancy) the species may be assessed as Vulnerable. Population size reduction is estimated in c. ≥ 30% as a conservative approximation.
Criterion B. According to current knowledge it is estimated that total area of occupancy is
< 2000 km2. The species is known from single populations in most of its distribution range but Spain where it is known from several localities. According to Mota et al. (2011) area of occupancy in Spain is not larger than 600 km2. Thus, total area of occupancy is smaller than 2000 Km2 (B2). Total number of locations is c. 10 (German record is doubtful) (B2a). It is clear that the range of this species has declined, at least in Spain -where most of the known populations occur- during the last century (B2b). Thus, it is estimated and inferred that there has been a continuous decline of (ii) area of occupancy, (iii) quality of habitat, (iv) number of subpopulations and likely (v) number of individuals during the last century. Since major threats have not stop (Mota et al. 2011) or even have increased, we project this trend will continue in the near future.
Criterion C. This criterion does not apply as no information about number of individuals and population size is available.
Criterion D. D1 subcriterion does not apply as no information about number of individuals is available. For D2 subcriterion AOO is larger than 20 km2 and number of populations is >
5, therefore the species is LC under D2.
Criterion E. This criterion does not apply as no quantitative analyses have been carried on.
Acarospora placodiiformis has been assessed as VU according to A2ac+ A3ac+ A4ac; B2ab(i,ii,iii,iv) at the European level.
According to FAO soils bulletin:62 there exist large extensions of gypsum soils in the North of Africa which have not been prospected for the occurrence of this species. Thus, we think that until the status of the species in those large areas are evaluated the species is assessed as Data Defficient at the world level.
Scattered localities in Spain (several localities, e.g. Atienza & Segarra 2000, Casares-Porcel & Gutiérrez-Carretero 1993, Crespo 1973), Greece (1 locality), Germany (1 locality, Stordeur 2006, Wirth et al. 2010), Iran (1 locality, Valadbeigi & Sipman 2010), Italy (1 locality, Nimis et al. 1996), Turkey (1 locality, John & Türk 2006) and Morocco (Casares-Porcel et al. 1994). Record from Germany is doubtful and should be checked and confirmed.
There are not estimates about population trends in any of the countries where it occurs. Best known populations are those from the Iberian Peninsula. Potential habitat has decreased considerably during the past century due to land use, especially area has been continuously decreasing due to the change of land use from grazing steppes to agricultural use. Further, mining for gypsum extraction is a current and actual problem as the number of mines has increased during recent years.
Population Trend: Deteriorating
It grows exclusively in gypsum soils together with other species also associated to this special kind of substrate. However, A. placodiiformis shows the smallest distribution range of this set of species.
The species shows a scattered and disjunct distribution, only known from less than 10 areas worldwide. Its habitat is threatened by multiple dangers, especially habitat destruction. This is due to changes in land use as traditional grazing in this gypsum continental steppes have changed along the years to a more agricultural landscape, in which gypsum associated species are being restricted to highly steep hill slopes where agriculture is not suitable. Further, gypsum, glauberit and thernadite mining, a non-stop activity since several centuries ago (especially gypsum mining), has increased its intensity during the last two decades. Urban pressure has also driven the loss of a large of its area especially in Central Spain, due to the proximity of the area to Madrid.
Finally, habitat in Central Spain where populations are likely the most exhuberant along its distribution range suffer of continous trampling due to cattle grazing and especially due to sport activities, mostly off-road motocycling.
Currently the species is not specifically protected in any country of its ditribution range but in Spain under the Regional Red List of the Valencian Community. In this community there is a micro preserve focused on the protection of a small gypsum area where this species occurs.
Some small areas in Spain are sites of community Importance (SCIs), although it has not been checked the extent or even the occurrence of the species in this protected areas.
Evaluate population sizes and connectivity among populations. It is neccesary to confirm the likely occurrence of the species in several countries of Northern Africa where large extensions of gypsum soils are reported. Potential threats in those areas as well as population sizes have to be evaluated.
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