This species is much more difficult to separate morphologically from Cerastium alpinum (Alpine Mouse-ear) that I had thought. The flower is slightly reflexed in C. arcticum but both are hairy with considerable variations possible in the hair features. The most convincing evidence is habitat. C. arcticum is an acid rock species with C. alpinum usually a calciole. This specimen is growing right out of the red granite of the Cairngorm on wet misty day when the visibility was only 30 or 40 metres. C. arcticum has more glandular hairs supposedly but the "glands" you can see in the photo are actually drops of water.

Access for this specimen meant first driving to the highest car park in the land at the Cairngorm Ski lift centre then following the track towards the Northern Corries. This track has improved immeasurably since I last came with solid granite stones laid into the path for quite a distance. Eventually though you have to cross boulder fields and near the cliffs of Coire an t-Sneachda where this species lives, the small rocks and pebbles are all unstable. Two sticks were vital. If you have any doubts about this type of expedition then don't go.

It is found mostly in Scotland with just one outpost in Snowdonia (where I haven't been able to find it yet.)