30 VEGETATION IN COLORADO-HOLM. [MemoieS [Vo L t .xix; 



Primula angustifolia Ton. and P. Parryi Gray. 



Both are natives of the higher Rocky Mountains of Colorado. The geographical distribu- 

 tion of the former extends to New Mexico, while the latter is known also from Nevada and Ari- 

 zona. Only a few other species are exclusively American, viz, P. suffrutescens Gray, P. Cusicki- 

 ana Gray, and P. Rusbyi Grne. (Oregon and Arizona). The other species of the genus which 

 inhabit North America are high northern, but they are more frequent in northeastern Asia 

 and Europe. There is thus in the Rocky Mountains a center of development of a few species 

 of Primula, but extremely poor in species when compared with the Alps of Europe and the 



mountains of Asia. 



THE GENUS ANDROSACE. 



In accordance with the table given above, Androsace Charruiejasme is almost circumpolar, 

 being absent only from Finmark, Spitzbergen, and Greenland. It occurs also in Switzerland, 

 and toward east the geographical range extends to the Caucasus, Baikal, Altai Mountains, and 

 the Himalayas. On this continent the range extends from Colorado northward to the coast, 

 from Bering Strait to the Archipelago. 



The other species, A. subumbellata, is known from Montana to Arizona and is endemic to 

 the Rocky Mountains. On this continent the genus is relatively poorly represented — by four 

 species according to Gray — but recently some three or four more have been described and 

 generally accepted. In the Alps of Switzerland the genus culminates with 13 species. Fur- 

 thermore, 7 are known from the Caucasus, S from Altai and Baikal Mountains, S from eastern 

 Siberia, 5 from Ural, etc. It would thus appear as if the geographical center of the genus 

 were to be sought in the Alps or in the Altai Mountains. As a matter of fact, the three sections 

 which have been established of the genus Aretia, Chamaejasme, and Haplorhiza are all repre- 

 sented in the Alps. The first of these, Aretia, is not known from Altai and Baikal but from 

 eastern Siberia. 



No doubt the European Alps may be considered a most important center owing to the large 

 number of species, including several endemic. Nevertheless the Rocky Mountains must con- 

 stitute another and of no smaller importance. For even if the genus in the Alps is accompanied 

 by a close ally, the monotypic Aretia, an ally so close that several authors have united it with 

 Androsace, there is on this continent another ally, Douglasia, with four species, which is also 

 closely related to Androsace. 



Concerning the distribution of Douglasia, D. nivalis Lindl., D. montana Gr., and D. laevigata 

 Gr. are endemic to the Rocky Mountains and the Cascade Mountains, principally at higher 

 elevations, while D. arctica Hook, is known only from the Arctic seashore. In other words, 

 these two genera, being Arctic or Alpine, may well be considered as representing a high northern 

 center of the Primulaceae. Douglasia arctica being a truly Arctic type and Androsace Chamae- 

 jasme being quite frequent on the Arctic shore, including the Archipelago, and sometimes 

 accompanied by A. septentrionalis and A. Gormani Grne., this little alliance may indicate a 

 former center located in the polar regions. Moreover, we remember that A. Chamaejasme is 

 almost circumpolar. 



The present more advanced development of both genera farther south in the Rocky Moun- 

 tains may have had its origin from an Arctic center. The fact that both A. Chamaejasme and 

 A. septentrionalis are known also from Altai and Baikal seems to indicate that they came from the 

 north. In Europe these same species migrated as far south as to the Alps and to the Caucasus, 

 where they still are in existence. The approximately circumpolar distribution of A. Chamae- 

 jasme in connection with the exclusively Arctic Douglasia. arctica thus seems to illustrate an 

 instance of a single center being located in the polar regions even if the genera in question are 

 at present more amply represented farther south, the former in mountains so remote as the 

 Alps, Caucasus, the Altai, the Himalayas, and the Rocky Mountains. And in these mountains 

 the genus has developed into several endemic species, which in spite of the enormous distances 

 offer an excellent illustration of " analogous endemism." 



