Sphagnum lindbergii, Schimp.

NEW POPULATION

On September 28, 2024, we found a new population of Sphagnum lindbergii View in CoL in the Spanish Central Pyrenees, specifically in Huesca, Chistau Valley, Montarruegos pastures ( Fig. 1 View FIG ), at elevations between 2145 and 2160 m a.s.l. We identified the species in the field and spent additional time searching for further patches. Our efforts led to the discovery of only four small patches in the Montarruegos area. Three patches were located near the coordinates 42°40’3”N, 0°18’29”E, and the fourth patch was at 42°40’14”N, 0°18’59”E (respectively ED50 UTM MGRS 31TBH72 and 31TBH82). In total, the species occupied an estimated area of only 5 m ², with the largest patch occupying approximately 3 m ². The maximum lineal distance between patches was 750 m. We conducted an exhaustive survey only of the Montarruegos valley, visiting all wet patches suitable for S. lindbergii (above the Sallena hut), where the species proved to be extremely scarce. However, we did not survey the nearby Tabernés area, where the species might also occur, although the available habitats there are smaller and more scattered.

This represents the first report of S. lindbergii in Spain and the Iberian Peninsula, and the second report for the Pyrenees, 32 years after Robert Gauthier and José Pujos found the first and only known French population ( Gauthier & Pujos 1999). The lineal distance between the French (las Honts, Rioumajou) and Spanish populations is approximately 2.8 km, so they might constitute a metapopulation complex, the only one known in the Pyrenees. In addition, this is the southernmost population in Europe ( Fig. 1 View FIG ). Besides the Pyrenean French population, the southernmost location is in the Austrian Alps, at a latitude of 47°N. Moreover, this is the only known population in the Alps, where the species is also extremely scarce. As can be derived from the above information, the species is absent from southern areas of Europe, including the Balkan and Italian peninsulas.

MORPHOLOGY

Sphagnum lindbergii is a well-established species with no significant taxonomic problems. It is readily identifiable as the only species in the subgenus Cuspidata that combines dark brown stems with large stem leaves (approximately 1 mm wide), which are broader near the fringed, tattered apex ( Daniels & Eddy 1990; Smith 2004). These characteristics can easily be checked in the field with a hand lens ( Atherton et al. 2010). Nevertheless, it is advisable to examine transverse sections of branch leaves under a microscope. The chlorocyst exposure is wider in the abaxial than the adaxial side, a feature common to all species in the Cuspidata subgenus. Our samples from Montarruegos exhibited all typical characteristics of the species ( Fig. 2 View FIG ), and their variation aligned with descriptions in the referenced literature ( Daniels & Eddy 1990; Smith 2004; Flora of North America 2024). We did not observe any fertile shoots.

ECOLOGY AND HABITATS

The new patches of S. lindbergii were located in the sub-alpine zone, avoiding south-facing slopes. In the area, sloping pastures on Ordovician schists formed the landscape matrix. There, S. lindbergii grew as dense moss clumps in flushes influenced by small rivulets flowing from iron-rich springs. The patches were found on steep, moss-covered slopes, sometimes even on vertical walls of the tiered mountainsides ( Figs 2F View FIG ; 3 View FIG ). This is of particular interest, as the species typically thrives in flat areas within boreal zones. Its occurrence here on steep slopes, avoiding southern exposure, may be related to increased shading and the resulting temperature-buffering effect. Although in Montarruegos similar habitats are present on nearby south-facing slopes, S. lindbergii is absent there. However, due to the extreme scarcity of the species, it is difficult to draw definitive conclusions. Furthermore, in French Pyrenean sites, the species has been observed both in flat areas and on steep slopes ( Gauthier & Pujos 1999; pers. obs. 18/09/2020). As for cooccurring species, the most common we found were Sphagnum species, particularly S. russowii Warnst. , S. tenellum (Brid.) Bory and S. fallax (H.Klinggr.) H.Klinggr. Other common accompanying species included Carex nigra (L.) Reichard subsp. intricata (Tineo ex Guss.) Rivas Mart. , Eriophorum angustifolium Honck. , Molinia caerulea (L.) Moench, and Polytrichum commune Hedw. The groundwater pH in the S. lindbergii patches was notably acidic, with a mean value of 4.1. The species displayed variable behaviour concerning water levels, thriving in conditions ranging from constantly wet vertical moss walls to waterlogged flushes. This matches the ecological conditions previously reported by Gauthier & Pujos (1999) for the French Pyrenees and Daniels & Eddy (1990) for the Scottish Highlands.

CONSERVATION STATUS

In the Pyrenees, S. lindbergii is confined to two valleys, one in France and one in Spain. In France, S. lindbergii is found in several patches in the Rioumajou Valley, where it is more widespread than in Montarruegos Valley ( Gauthier & Pujos 1999; pers. obs. 18/09/2020). However, there it remains extremely scarce and is therefore classified as critically endangered (CR) according to IUCN criteria ( Infante Sánchez et al. 2015; IUCN Standards and Petitions Committee 2024). Applying the same criteria, we consider S. lindbergii to be critically endangered (CR) in Spain and recommend its inclusion in the regional and national lists of threatened species. The species in Spain meets the following criteria: an extent of occurrence of less than 100 km ² (B1), an area of occupancy of less than 10 km ² (B2), and a population size of fewer than 50 individuals (D), resulting in a conservation status of CR B(1+2)ab(iii)D1. According to Garilleti & Albertos (2012), we considered each discrete differentiable unit as an individual. We might consider these two close French and Spanish populations as part of a single metapopulation. However, it is not clear whether a migration of propagules from French to Spanish side (i.e. a rescue effect) could occur, as the sporophytes are absent ( FLORAPYR 2019) and consequently it should disperse vegetatively.

In addition to climate change, a primary threat to S. lindbergii in Montarruegos is livestock grazing, and indeed, we found severe trampling in some mire areas. This could potentially affect flushes where S. lindbergii is present, and therefore, land managers should take steps to mitigate this threat. Unfortunately, the Montarruegos Valley lies just outside the boundaries of the Posets-Maladeta Natural Park and is also just outside the Natura 2000 Sites of Community Interest, which may hinder effective monitoring and conservation measures for the species in Spain.