Panarctic Flora

420205-11 The Cerastium alpinum aggregate C. aleuticum, C. alpinum, C. arcticum, C. beeringianum, C. fischerianum, C. nigrescens, C. regelii

Geography: Circumpolar-alpine.

Notes: Elven and Brysting: The Cerastium alpinum aggregate is a large arctic-alpine polyploid complex for which two main evolutionary models were proposed many decades ago. Hultén (1956 and elsewhere) considered it "a case of worldwide introgressive hybridization", whereas Böcher (1977) considered it "a mature polyploid complex". Studies in recent years have largely given support to Böcher's model (Brysting and Hagen 1999; Brysting and Borgen 2000; Brysting and Elven 2000; Brysting et al. 2007a, 2007b). Parts of the variation, especially in the broadly amphi-Beringian regions, are still unresolved but some headway has been made (Brysting et al. 2007b). Sequence data (Scheen et al. 2003) suggest that this aggregate has developed recently (Pleistocene and later) and with comparatively little molecular divergence yet. It may not be as "mature" as Böcher (1977) thought but the widespread introgressive hybridization proposed by Hultén (1956) seems to be absent (even if primary hybrids are frequent). The paths of several low-ploid genomes into the high-ploids have now been mapped (Brysting et al. 2007b).

The taxa we accept as species are morphologically separable. However, the name C. alpinum has frequently been used in a very collective meaning, especially in North America and Greenland (there as recently as, e.g., Bay 1992). Older records are therefore often difficult to assign to the species we currently accept.