36 VEGETATION IN COLORADO-HOLM. [Memoir * y^mx 



GRAMINEAE."* 



The following species in Colorado are confined to the Alpine region: Agrostis canina L. 

 var., A. varians Trin., Avena Mortoniana Scribn., Poa jlexuosa Wahblenb., P. gracillima Vas., 

 P. Fendleriana (Steud.), P- Lettermannii Vas., P. alpina L., Festuca ovina L., var. supina 

 Hack., Agropyrum Scribneri Vas., and A. violaceum Lge. The remaining species, on the other 

 hand, were also observed at lower elevations, from the aspen zone to the spruce zone. PJiUum 

 alpinum L., for instance, descends to the aspen zone on Longs Peak, where it is very frequent 

 in swamps. Calamagrostis purpurascens R. Br. follows the creeks throughout the spruce zone 

 on Longs Peak and the region of Clear Creek Canyon. C. canadensis var. acuminata Vas. is 

 only exceptionally Alpine and thrives best in the swamps of the aspen zone. Deschampsia 

 caespitosa Beauv. is most frequent and typically developed in swamps of the aspen zone, but 

 is also very common near snow banks at high elevations. Trisetvm suhspicatum Beauv. does 

 not descend much farther than just to the timber line. Poa rupicola (Vas.) Nash descends 

 to the aspen zone on James Peak and near Central City, but only seldom. Festuca ovina L. 

 was collected in the aspen zone near Central City, and in the spruce zone on Mount Massive 

 and Longs Peak. 



Four of these Alpine species are circumpolar : Trisetum,Poa jlexuosa,P. alpina, Festuca ovina, 

 and the var. supina. Calamagrostis purpurascens is the only one that is confined to this conti- 

 nent and Greenland. Agropyrum violaceum occurs in the Arctic regions of both hemispheres, 

 and Festuca ovina var. supina is also an inhabitant of these high northern regions outside America. 

 All the others extend to the mountains farther south, and five of these have even reached the 

 Himalayas. The Alpine Gramineae in Colorado thus represent an assemblage of several very 

 distinct geographical types — some that are endemic to this particular region; some that occur 

 also on the Pacific and Atlantic coasts; some that have reached the polar regions in certain 

 parts of both hemispheres; some that are circumpolar; and, finally, some that have become 

 dispersed throughout the mountainous districts farther south in Europe and Asia. 



The circumpolar species originated undoubtedly in the polar regions. But Calamagrostis 

 purpurascens developed evidently in the Rocky Mountains and migrated with the Arctic 

 flora to Greenland. Agropyrum violaceum, on the other hand, may have originated in the 

 Arctic. PMeum alpinum, being much more frequent in the mountains of the temperate 

 regions, did evidently develop there, but the occurrence of this plant in the Baikal Moun- 

 tains and in the Himalayas and its absence from Arctic Siberia, beside its wide distribution 

 in Europe and on this continent, seems to call for more than one center of geographical 

 distribution. The species endemic to the Rocky Mountains naturally developed there. 



The occurrence of Juniperus communis in the Arctic regions, as a depauperate form, however, 

 may be considered as an indication of migration toward the north when the ice receded. The 

 species, being so widely distributed farther south, naturally developed there, although it is not 

 possible to locate the actual center. 



By comparing the geographical distribution of these Alpine species, in order to locate the 

 probable center of their distribution and development, it seems safe to conclude that the 

 endemic species originated in the Rocky Mountains ; that the circumpolar and a part of the^ 

 Arctic element came from the Arctic regions; that several of the species, known also from 

 various districts of the temperate zone, may have developed from more than a single center, 

 at least in cases where the present distribution is extremely wide but at the same time inter- 

 rupted by gaps of immense extent, the actual cause of which can not be satisfactorily 

 explained. 



« Holm, Theo: The Gramineae of the Alpine region of the Kocky Mountains in Colorado. (Bot. Gazette, 46:122. Chicago, 1908.) 



