Cryophytes, polyploidy, and continental drift
Löve, Áskell; Löve, Doris
The plant cover of the tundras of high altitudes and latitudes is composed of less than 3000 species of socalled cryophytes, which belong to many families and numerous genera of vascular plants. At altitudes and latitudes higher than the tundra of mountains and lowlands are the barren lands where no higher plants persist; this is above 6-7000 meters altitude in the Tropics and at about 85°N and 60°S respectively. The cryophytes are rarely trees or annuals and predominantly chamaephytes or hemicryptophytes. Among their most significant biological characteristics is their high frequency of polyploidy, which is an important mechanism of speciation and also one of the most prominent preadaptive conditions known. It is emphasized that polyploids and other prospective cryophytes were mainly formed in lowlands with equitable climates, but when selection decreased the number of species in a flora, either by uplift of mountain chains or by drift of the continents into severe climatical conditions, these plants were favored and their frequency increased. Alpine plants have been formed at all times in all climates when mountains were formed. However, only some of these later found their way to the extreme climates of the northernmost and southernmost of lands, whereas most arctic plants, which constitute more than half of all the cryophytes, were formed by selection at the time the nemoral flora was severely reduced when it was forced into the arctic regions on the drifting continents in the Oligocene. They were further molded into the highly polyploid and generally rigid flora of the northlands by the successively colder climates which culminated during the Pleistocene.