Tortella rigens (Bryophyta, Pottiaceae): relationships, regional variation, and conservation aspects

Abstract

Tortella rigens occurs in the European Baltic region and at a few localities in North America. At least 95 % of all localities are found in southern Sweden. It is morphologically similar to the more widespread T. bambergeri, which was found in Sweden during this study. Haplotype networks, based on ITS or the chloroplast markers atbB-rbcL and rps4, for T. rigens, T. bambergeri, and closely related species display significant reticulation and NeighborNet and Jacknife analyses are used to explore the species’ relationships. Significant incongruence is found between the two molecular data sets or between these and the morphologically defined species, and several species appear polyphyletic or paraphyletic. Sporophytes of T. rigens are described and appear to be a result of hybridisation, which could partly explain the reticulation. Among the four South Swedish T. rigens populations, those of Gotland (GTL) and the Stockholm archipelago (SAR) are not differentiated molecularly from each other and there are signs of significant migration between them. The ones in Vastergotland (VAS) and Oland (OEL) are distinct from each other and from GTL and SAR. The haplotype pattern of GTL displays signs of population increase whereas a decrease is found for VAS. Although the time scale is uncertain, this decrease is of conservation concern, considering that VAS has one unique haplotype. OEL has both the highest number of unique haplotypes (4) and the highest haplotype diversity of all four populations and has therefore the highest importance for conservation. Tortella rigens and T. bambergeri can be differentiated by atpB-rbcL.