Yellow Saxifrage (Saxifraga aizoides) flowers much later. The picture below was taken on 4th July 2007.
In Greenland, the summers are so short that they may be in flower at the same time. In a small area of East Greenland, one can find Saxifraga nathorstii, which is thought to be a hybrid of the two species which has doubled its chromosome number and become able to produce seed. The colour is intermediate between the other two species.
The picture below shows S. oppositifolia to left and right, S. nathorstii 2nd from left and S. aizoides 3rd from left. I took this photo near Mestersvig in East Greenland in early July, 1983.