RYDBERG: PHYTOGEOGRAPHICAL NOTES 4A7 
Castilleja confusa Eucephalus formosust 
Castilleja rhexifolia Aster adscendens 
Castilleja trinervis Erigeron yellowstonensis 
Pedicularis Parryi Erigeron subtrinervis 
Pedicularis crenulatat Antennaria viscidula 
Galium flaviflorumt Anaphalis subalpina 
Oreochrysum Parryit Helianthella Parryit 
Eucephalus wasatchensis} Arnica mactlentat 
Eucephalus glaucus} 
IV. POPLAR GROVES © 
These are found in the narrower valleys and cafions, where 
there is a certain amount of moisture, but where the ground is 
comparatively well drained. The principal tree is the narrow- 
leaved poplar or cottonwood, Populus angustifolia. Another 
common tree is Salix Scouleriana, and Young* has called this for- 
mation the Populus angustifolia—Salix Nuttallii Formation. 
Another common tree is the smooth maple, Acer glabrum. The 
balsam poplar, Populus balsamifera, has been collected in a few 
places in Colorado, and the canoe birch, Betula papyrifera 
(B. Andrewsii), has been collected in one cafion. Some of the 
evergreens have also partly invaded this formation, as Pseudotsuga 
mucronata and Abies concolor, and a few species of hawthorn are 
found in the lower part of the zone. In the Foothills (Submontane 
Zone) the narrow-leaved cottonwood is replaced mostly by 
Populus acuminata and P. Sargentii. The undershrub and 
herbaceous vegetation contains many species found in the Aspen 
Groves. 
I. TREES AND SHRUBS 
a. Eastern 
Populus balsamifera Betula papyrifera 
Salix Bebbiana ; Dasiphora fruticosa 
b. Western 
Pseudotsuga mucronata Cercocarpus ledifolius 
Salix Scouleriana Rubacer parviflorum 
Ribes viscosissimum Rubus melanolasius 
* Bot. Gaz. 44: 334-336- 1907. 
