The arctic mouse-ear in Scotland – and why it is not arctic

Abstract

Background : The arctic mouse-ear (Cerastium nigrescens, Caryophyllaceae) growing in the Scottish Highlands has a turbulent taxonomic (and nomenclatural) history, probably reflecting the complex allopolyploid origin of this high-polyploid species. It belongs to an intricate arctic-alpine species group (the C. alpinum complex) which has a reticulate evolutionary history formed through repeated hybridisation and polyploidisation events. Aims : In this paper, the position of the Scottish plant is discussed in the light of recently published sequence data from the whole complex. Methods : Sequences of a low-copy number nuclear gene (RPB2) of a few Scottish plants were obtained and compared to previously obtained sequences of C. nigrescens from other geographical areas, other closely related high-polyploid species as well as possible tetraploid progenitor taxa. Main findings : A network produced from the RPB2 sequences clearly showed that the dodecaploid plant growing in the Scottish Highlands has a common origin with C. nigrescens from Scandinavia and Shetland. By using the same approach, it was also possible to identify hybrids among Scottish plants resulting from interploidal crosses between C. alpinum (8x) and C. nigrescens (12x). Such hybrids possessed a combination of RPB2 sequences from these two parental species. Conclusions : The Scottish C. nigrescens shares its evolutionary history with C. nigrescens from Shetland and mainland Norway, and this non-arctic taxon is clearly separated from the artic taxon, C. arcticum, with which it has previously been considered conspecific.