Identity and relationships of Sempervivum tectorum (Crassulaceae) in the Rhine Gorge area

Armin G Fabritzek,Joachim W Kadereit

doi:10.3372/wi.48.48310

Abstract

Sempervivum tectorum (Crassulaceae), an orophyte widespread in the European high mountains, also grows in rocky habitats of the Rhine Gorge area (Upper Middle Rhine, Mosel and Ahr river valleys). On the background of its long history of cultivation, it is unclear whether S. tectorum is native or naturalized in the Rhine Gorge area. Using 52 accessions of S. tectorum from across its geographical range (except SE Europe) as well as 15 samples of S. calcareum and S. marmoreum in our final sample, we conducted a genotyping-by-sequencing analysis. The genetic data were used for the identification of genetic groups and for the reconstruction of phylogenetic relationships. We found that the material from the Rhine Gorge area forms a homogeneous genetic group that is clearly distinct from populations from the Massif Central, Alps and Pyrenees. The Rhine Gorge material appears to be most closely related to material from the Massif Central. We hypothesize that the disjunct distribution of the Rhine Gorge/Massif Central clade is best interpreted as the remnant of a formerly wider distribution area obtained in a Quaternary glacial. The possibility of recognizing Rhine Gorge material taxonomically is discussed and rejected for morphological and nomenclatural reasons.

Highlights

The various rocky habitats of the Rhine Gorge area, here understood to comprise the Upper Middle Rhine, Mosel and Ahr river valleys, harbour a number of species that outside this area are distributed disjunctly mainly in the Alps and other European high-mountain ranges
We found that the material from the Rhine Gorge area forms a homogeneous genetic group that is clearly distinct from populations from the Massif Central, Alps and Pyrenees
The mean number of loci in the final data set shared among all samples was 4239 with a standard deviation of 1102. These loci contained a total of 28 387 single nucleotide polymorphism (SNP)

Summary

Introduction

The various rocky habitats of the Rhine Gorge area, here understood to comprise the Upper Middle Rhine, Mosel and Ahr river valleys, harbour a number of species that outside this area are distributed disjunctly mainly in the Alps and other European high-mountain ranges. These include, e.g. Amelanchier ovalis Med., Biscutella laevigata L., Cotoneaster integerrimus Med., Rumex scutatus L. and Sempervivum tectorum L. Following Lippert (1995), this decree refers to S. tectorum and most likely is based on the widespread belief that the species protects against lightning and fire On this background, the native status of S. tectorum in the Rhine Gorge area has been discussed (Hayek 1922) or doubted (Jäger 2011). S. tectorum is rare, and of all known populations only 12 grow at sites considered natural by us (see below)

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Conclusion