PLANTS IN ARCTIC-ALPINE ENVIRONMENT — SHETLER 493 



Whatever the true relative frequency of polyploidy on the earth's 

 surface, we must reckon with the fact that the number of species ex- 

 hibiting some polyploidy within their ranks may reach as high as 80 

 percent of the total flora in certain arctic areas. Perhaps the ex- 

 planation lies in an ability of polyploids to tolerate more extreme 

 conditions, as has usually been suggested, but certain other facts 

 tend in part to explain this high percentage quite apart from their 

 ecological tolerance. These facts cannot be overlooked in any at- 

 tempt at generalization. First, the families Gramineae (grasses) and 

 Cyperaceae (sedges) are known to have an unusually high incidence 

 of polyploidy among their species, and these particular families com- 

 prise a relatively large segment of the arctic flora, as already noted. 

 Second, polyploidy is also particularly frequent among herbaceous 

 perennials with efficient means of asexual reproduction, such as tend 

 to dominate the arctic flora. Third, glaciated areas tend to be higher 

 in polyploids than unglaciated areas, and a large segment of the 

 present-day arctic flora occupies glaciated land. The presumption 

 is that polyploids are better early colonizers. In smnmary, then, the 

 explanation for the apparently high incidence of polyploidy in the 

 Arctic may be far more indirect and complex than has been thought. 



The second consideration above raises the question of apomixis, 

 which in the strict sense refers to the production of viable seeds 

 parthenogenetically (without fertilization by male), and in the broad 

 sense includes all asexual means of reproduction. In either sense, apo- 

 mictic species are uncommonly frequent in the Arctic. What's more, 

 an apomictic species is very likely to be polyploid, and many poly- 

 ploids are apomictic. This correlation is not necessarily unexpected. 

 A polyploid species can escape all the cytological difficulties of normal 

 seed production that usually attend polyploidy, if it reproduces by 

 some asexual means instead. In other words, an apomictic "bypass" 

 of sexual reproduction permits certain polyploid biotypes that would 

 ordinarily be eliminated rather quickly to survive and even to thrive 

 and spread. Clearly, apomixis is advantageous to arctic-alpine plants, 

 and apomictic biotypes would tend to accumulate in these harsh en- 

 vironments over a long period of time. Thus, we can understand 

 how apomixis would be an adaptation for arctic-alpine environments 

 and how polyploidy can survive in apomictic households, but this 

 still leaves open the real question of the selective advantage of poly- 

 ploids in the Arctic, if any. 



FLORISTIC AND GEOGRAPHICAL ASPECTS OF ARCTIC-ALPINE VEGETATION 



If from an ecological viewpoint the vegetation of the arctic-alpine 

 environment is unique, what about the individual species that com- 

 prise it? To what degi-ee is the flora of the Arctic- Alpine unique? 



