26 VEGETATION IN COLORADO-HOLM. [Memoiks [ vol T .x1x i : 



S. chrysantha Gr. 



This is known only from Colorado. A near ally, S. serpyllifolia Pursh, occurs in Alaska, 

 on the Asiatic coast of Bering Strait, and in the Altai Mountains. Besides that the variety 

 Palassiana Sternb. is recorded from Arctic Siberia and Baikal. 



S. bronchialis L. 



Through Arctic Russia and Siberia this species extends to Altai and Baikal, to Kam- 

 chatka, Alaska, and follows the Rocky Mountains as far south as New Mexico. A near ally, 

 S. tricuspidata Rottb., is a native of Arctic America and Greenland. 



S. flagellaris Willd. 



This polymorphous species is widely distributed in the Arctic regions, from whence it extends 

 to the Caucasus, the Himalayas, Altai, and Baikal Mountains, as well as in Colorado. It is the 

 typical plant that occurs in Colorado, but according to Engler (1. c.) the variety setigera 

 Pursh has also been reported from this continent, Baffins Bay, Melville Island, Alaska, and 

 the Rocky Mountains. 



S. punctata L. 



This species is not circumpolar, but has been reported from Arctic Siberia and North 

 America, extending south to Ural, Baikal, Cascade Mountains, and the Rocky Mountains. 



S. nivalis L. 



Circumpolar and known also from Great Britain, Norwaj*, Sweden, Germany, Baikal 

 Mountains, Kamtschatka, Canada, Greenland, and south to Colorado. 



Of these the circumpolar species are evidently of Arctic origin, but became widely dis- 

 tributed during and after the glacial epoch. S. chrysantha, is a native of Colorado, while 

 its near ally, S. serpyllifolia Pursh, is distributed in regions much farther north, Alaska, 

 and the Baikal Mountains. The geographical center of the latter may have been in these 

 mountains. S. Ironchialis shows quite a wide range in the Arctic regions, but the geographical 

 center was evidently somewhat farther south, the mountains of Altai and Baikal. We 

 remember that most of the other species of Traclryphyllum are endemic to the Himalayas. 

 With regard to S. punctata, this may, similar to S. bronchialis. have originated in the Altai 

 and Baikal Mountains. 



Oreoxys humilis Raf. and O. alpina (Gr.) C. et R. 



These species, together Math 0. BaJceri C. et R., are natives of the Rocky Mountains, Colo- 

 rado, and are well represented in the high Alpine regions. It is interesting to note that the 

 genus has two analogues in the Old World, namely, Gaya Gaud, and Pachypleurum Ledeb., 

 of which G. simplex Gaud, is a native of the Alps of Switzerland; it has also been reported from 

 Arctic Russia and Altai; Pachypleurum alpinum Ledeb. is, on the other hand, known from 

 Arctic Russia and Arctic Siberia, and from the mountains of Altai and Baikal. We have thus 

 among the Umbelliferae three allied genera, one of which is purely Alpine and of North 

 American origin, the remaining two being Arctic-Alpine. 



Among the Compositae we meet with several species of which the geographical distribution 

 is of interest. Some of the Alpine types are also Arctic and even circumpolar, while others 

 are confined to the Rocky Mountains. 



The genus Erigeron is represented by E. salsuginosus Gr., E. unifiorus L., and E. pinnati- 

 sectus (Gr.) Nels. Of these the first species has been recorded from Kotzebue Sound and 

 Unalaska, and it follows the higher mountains southward to California, Utah, and New Mexico, 

 and the variety glacialis (Nutt.) Torr. et Gr. occurs in the Alpine region of the Rocky Moun- 

 tains. E. uniflorus L., on the other hand, is circumpolar, and is also widely distributed in 

 the boreal regions of this continent, from Labrador to the Arctic coast and Unalaska, south 

 to Sierra Nevada, California, and Colorado. It occurs also in the Altai and Baikal Mountains 



