92 Rydberg: Phytogeographical notes 



4. Eurasian alpine plants, found in the mountains of the Old 

 World, but not in the arctic regions. The principal subdivisions 

 of this group are: 



(a) Alpestrian, endemic plants of the European Alps, including 

 the Pyrenees and the Caucasus; 



(b) Altaic, north Asiatic alpine plants. 



5. American endemic alpine plants. The principal regions of 

 these are the following: 



(a) Sierra Nevada, including the Cascade Mountains, which 

 latter, however, contain an intermixture of some elements belong- 

 ing to the next; 



(b) Rocky Mountains, including the San Francisco Mountains 

 and the other ranges of Arizona, New Mexico and northern 

 Mexico ; 



(c) White Mountains. Most of the plants of this region belong 

 to the arctic-alpine group, but endemic alpine plants are not 

 wholly lacking, as for instance, Potentilla Robbinsiana and Sieversia 

 Peckii. 



6. Circumpolar arctic plants, not found in the mountains. 



7. Eurasian arctic plants, which do not concern us at all. 



8. American arctic plants. 



9. Subarctic and 



10. Subalpine plants, which encroach on the arctic and alpine 

 regions. 



Circumpolar Arctic-alpine or Glacial Plants 



These species probably had originated before or during the 

 glacial epochs. In some cases the origin probably was somewhere 

 in the Old World, in others in the New World. Of course, we cannot 

 know, but we may surmise. The region which contains the most 

 numbers of certain groups of species may probably be the place 

 where this group originated (i. e. the home of the parent species) 

 and where the individual species sprang from. As for instance, 

 there is a group of arctic-alpine species of Potentilla with ternate 

 leaves white-wooly beneath. Potentilla nivea is the most generally 

 distributed species of the group; it is also the first and best known. 

 Where is the probable ancestral home of this species? The species 

 is found in Europe, rather common in the Scandinavian mountains, 



