The cold, dry semideserts which exist across the north end of Greenland and the northern and western Canadian Arctic Archipelago place very different stresses upon their vegetation than in the other deserts of the more southerly lattiudes. The long dark season and correspondingly long light season rather than diurnal changes, and the low angles of the light which yields 69% in long wave radiation and only 50% of global radiation in the shorter waves available for photosynthesis, representing 16% of the total incoming radiation (Addison & Bliss, 1980) place quite different stresses upon the lichens than in other deserts. Further problems are caused by the permafrost and frost perturbations. At these high latitudes the areas covered by vegetation may be exceedingly restricted. Yet on the vegetated portions the lichens may constitute a large percentage of the ground cover,15-40% on Devon Island beach ridges (Barrett & Thomson, 1975) or 40% on King Christian Island (Addison & Bliss,1980). At Cornwallis Island it was quite obvious that the greater part of the island was unvegetated and the lichens were best represented in the erosional drainage channel areas caused by the rapid drainage of the spring meltwaters so characteristic of the arctic. On other islands as Victoria Island and Baffin Island much richer cover and floras exist where there is greater moisture and longer seasons.