﻿Rydberg: Phytogeographtcal notes 13 



much closer to the Rockies, and separated from the Cascades by 

 the Columbia and Frazer River valleys, have a flora resembling 

 that of the Cascades as much as that of the Rockies. This 

 Cascade flora, however, extends also to the western slopes of the 

 Rockies in British Columbia and northern Montana as well as 

 into the Bitter Root Mountains between that state and Idaho, 

 although the Bitter Roots are separated from the Selkirks by the 

 valleys of Kootenay River and Clark's Fork. 



This division between Northern and Southern Rockies is not 

 made merely on geographical grounds, i. e., because there is a 

 break in the high mountain chain where the plains actually cross 

 over the continental divide. The flora shows also many dif- 

 ferences; this is especially the case with the more characteristic 

 species, the trees. It is true that a number of these are common 

 to the Northern and Southern Rockies, as, for instance, Picea 

 Engelmannii, Pinus scopulorum, Pinus Murray ana, Pinus flexilis, 

 Pseudotsuga mucronata, Abies lasiocarpa, Sabina scopulorum, 

 Betula fontinalis, Alnus tenuifolia, and several species of Crataegus, 

 Salix, and Populus; but others are not. 



Pinus aristata, P. edulis, Picea Parryana, Abies concolor, 

 Sabina utahensis, S. monosperma, Populus Wislizeni, P. Fremontii, 

 Fraxinus anomala, and the oaks of the Quercus Gambellii and Q. 

 undulata groups are characteristic of the Southern Rockies. Of 

 these only Picea Parryana has been collected in what belongs to 

 the Northern Rockies. The only authentic locality there that I 

 know is in the Teton Mountains, and these are, as stated before, 

 in the region where the two floras meet. Abies concolor extends 

 into the Bear River Mountains but does not cross the line, al- 

 though it is found much farther north in western Oregon. It 

 has been reported from other parts of Idaho, but evidently has 

 been confused with A. grandis, at least all specimens I have seen 

 named A. concolor belong to that species. Sabina utahensis is 

 found on the southwestern slopes of Wind River Mountains in the 

 Green River basin, but this species belongs to the foothills and 

 not to the mountains proper. The only oak found in the Northern 

 Rocky Mountain region is Quercus macrocarpa, and this only in 

 the Black Hills. It is not found in the Southern Rockies and it 

 is an invader from the prairie region. The same can be said 



