Strand and Dune Flora of the Pacific Coast 173 



verse in superficial aspect, which have been described by various 

 authors as separate species. The species as a whole ranges over 

 North America, Asia, Europe, and Northern Africa. Hall recog- 

 nizes six subspecies, all o£ which have consistent ranges. Subsp. 

 pycnocephala is the most distinct and is isolated in range from 



the others. 



DISCUSSION 



Species of Strand and Shifting Dunes 

 geographic relations 



Of the 25 species of strand and moving dunes, 12 range beyond 



the region under discussion in various directions, and 13 are 



endemic. The 12 with extraterritorial ranges fall into five groups. 



Discussion of these and of the endemics will be followed by 



generalizations concerning the origins of the strand and shifting 



dune flora. 



1. Species tvith more or less perfect circumpolar distribution, 



ranging various distances southward along the coasts of the 



Atlantic and Pacific. 



Elymus arenarius Lathy rus japonicus 



Honckenya peploides Mertensia maritima 



We have no certain knowledge of the preglacial distribution of 

 the species of this group. We may, however, point to certain places 

 where they may have survived during the period of Pleistocene 

 glaciation. The southern parts of their coastwise ranges on the 

 Atlantic and Pacific immediately suggest themselves. In addi- 

 tion, there is no apparent reason why they may not have lived 

 upon the Arctic coasts of America and Siberia. In Alaska, except 

 in the southern part, the lowlands and shores were ice-free. 

 Elymus, Honc\enya, and Mertensia live today upon the shores 

 of Greenland, where the edge of the ice sheet lies very close to 



