Arabis petraea Northern Rock-cress R DDD N
Re-directed to Arabidopsis petraea following name change.
I find A. petraea on ledges or growing out of cracks on mountain rocks and because it is one of many similar white crucifers, you need to get close for a positive identification which isn't always easy. The flowers are not entirely dissimilar to A caucasica (Garden Arabis) which grows abundantly on the limestone rocks of the White Peak in Derbyshire, but the leaves are quite different. This plant was very conveniently only 4 feet off the ground growing out of a crack on cliffs below Snowdon summit.
Arabis petraea is absent from England and only occurs in Snowdonia in Wales. Apart from a couple of sites in Ireland the rest of the population are to be found in Scotland most frequently on the Cairngorms and on the mountains of Skye.