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 rocks 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. Drummondit, 
and smaller colonies of Potentilla quinquefolia 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 
acaulis, 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 Sedum 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. 
multifidus. 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. £. 
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, 
sg ipo ran Nis a a 
