462 Rydberg: Phytogeographical notes 



very low, only a few inches high, buc what they lack in size they 

 make up in the coloration of their flowers. It is strange that the 

 alpine plants should have such bright colors, when insects are 

 comparatively rather scarce and the plants have all the facilities 

 of wind-pollination. Most of the plants of this formation grow 

 in clumps or mats, even the grasses and sedges growing there are 

 more or less tufted. 



One of the most common and, at the same time, conspicuous 

 plants of this formation is Alsinopsis obtusiloba. It is not con- 

 spicuous on account of its size or the beauty of its flowers, but on 

 account of its mode of growth. It is found nearly everywhere in 

 the most exposed places, in the crevices of the rocks or between the 

 boulders, wherever the roots can find a foothold, even where there 

 is scarcely a trace of soil. It grows in tussocks or mats from I to 

 12 inches in diameter, the stem lying flat on the recks and only 

 the peduncles rising 1-2 inches above them. Draba oligosperma, 



D. andina, and D. densiflora have a similar habit but grow in 

 smaller mats and are more frequent between smaller stones and 

 gravel on the ridges. In similar situations are found larger mats 

 of Dryas octopetala and (in the northern Rockies) D. Drummondii, 

 and smaller colonies of Potentilla quinquejolia and Phlox caespitosa. 

 The latter is rather rare in the southern Rockies where its place is 

 taken by a closely related species, Phlox condensata. Silene 

 acaidis, the moss campion, resembles Alsinopsis obtusiloba in 

 habit, but prefers places with more humus. The vegetation of 

 the bare rocks consists mostly of the above mentioned Alsinopsis 

 and less frequently Sednm stenopetalum and scattered patches of 

 Draba and Phlox. 



Two of the most widely distributed plants growing in gravelly 

 places on the tops of the mountains are Erigeron simplex and E> 

 mnltifidus. The following three species, closely related to the 

 latter, are found in similar situations, but E. trifidus is more limited 

 to the northern portion, extending even into the Arctics. E. 

 pinnatisectus is confined to the southern Rockies and the original 



E. compositus to the northwest. In similar situations we find also 

 Smelowskia americana and Trifolium dasyphyllum; in the southern 

 Rockies also Androsace carinata, Thlaspi coloradense, T. pur- 

 purascens, and Eritrichium argenteum; and in the northern Rockies, 



