Molecular analysis of the extinct Central European endemic Saxifraga oppositifolia subsp. amphibia and its implications on glaciation biogeography

Extinction of biodiversity due to human activities is a severe global problem. In Europe, however, only a few plant species died out so far. We investigated a dubious, disregarded taxon— Saxifraga oppositifolia subsp. amphibia —which became extinct in the 1960s. It exclusively occurred in a specific niche, namely in seasonally flooded waterside bank vegetation around Lake Constance in Germany and Switzerland. It has either been interpreted as a glacial relict or as a recent dealpine taxon. Using herbarium material, we conducted phylogenetic analyses based on ITS and cpDNA sequence variation. The taxon shared a chloroplast haplotype of S . oppositifolia , which is mainly distributed in the Alps, favouring the dealpine hypothesis. Nuclear data revealed several paralogous copies nested inside S . oppositifolia , most of which, however, differed from other S . oppositifolia accessions including those from the vicinity of Lake Constance. The oldest mean stem node ages of these ITS copies date between 0.91 and 0.28 my. Contradicting cpDNA, this may indicate that this saxifrage was a distinct taxon and possibly a relict originating in Middle Pleistocene glaciations. If so, the present study exemplifies that arctic-alpine plants survived in specific niches at low altitudes during interglacials and that corresponding taxa with a limited distribution are especially prone to extinction.