THE SILVA OF COLORADO 53 
its range this tree grows with limber pine and at higher altitudes with Engelmann spruce. 
Scattered trees are found to the upper limit of wind-blown timber on all the peaks. Seldom 
used for lumber; the wood is weak and brittle. 
Altitude: 8,000 to 11,500 ft. Collections: Eldora; Ward; foot of Mt. Audubon. 
JUNIPERACEAE, JunirPEer FAmiLy 
Juniperus sibirica Burgsd. JUNIPER 
A prostrate spreading shrub with sharp-pointed leaves. Dry situations on mesas 
and foothills to the base of the main range. 
Altitude: 6,000 to 10,000 ft. Collections: South Boulder Canyon, 6,800 ft.; above 
Magnolia; Sugarloaf; Eldora; foot of Long’s Peak; Gresham; “mountains between 
Sunshine and Ward” (Rydberg). 
Sabina scopulorum (Sarg.) Rydb. CEDAR, RED CEDAR 
A small conical tree, or in wind-swept places much distorted. Usually in exposed 
situations on hills and ridges; formerly used for fence posts, but the supply now exhausted. 
Altitude: 5,000 to 8,500 ft. Collections: Bluebell Canyon; South Boulder Can- 
yon 6,800 ft.; above Magnolia; Sugarloaf. 
SMILACEAE, Smitax FAmItLy 
Nemexia lasioneuron (Hook.) Rydb. SmILAx, CARRION FLOWER 
A low, trailing plant of shady situations growing under trees and bushes. 
Altitude: 5,000 to 6,500 ft. Collections: mouth of Boulder Canyon; mouth of 
Gregory Canyon. 
SALICACEAE, WILLow Famity 
Populus acuminata Rydb. LANCELEAF COTTONWOOD 
A medium-sized tree of somewhat symmetrical form rather rare in Boulder County 
except where planted. Along streams. 
Altitude: 4,900 to 6,000 ft. Collections: gulch one mile south of Chautauqua; 
Valmont; cultivated at Boulder. ~ 
Populus angustifolia James. NARROWLEAF COTTONWOOD 
A tree of open, unsymmetrical form growing along streams. Very common. 
Altitude: 5,000 to 9,000 ft. Collections: 17th Street bridge at Boulder; Boulder; 
South Boulder Canyon; Valmont; mouth of Gregory Canyon; “Boulder” (Rydberg). 
Populus balsamifera Linn. BALM oF GILEAD, BALSAM POPLAR 
A medium sized tree of gulches and along streams. 
Altitude: 8,000 to 10,000 ft. Collections: Fouth of July Mine; Eldora; Allenspark. 
Populus sargentii Dode. Common WESTERN COTTONWOOD 
This is Populus occidentalis of Rydberg’s Flora and P. angulata of Coulter’s Manual. 
Common along streams in the plains region and occasional in the mountains. Much 
planted for shade. 
Altitude: 4,900 to 8,500 ft. Collections: Valmont; Boulder Creek; Boulder; 
mouth of Gregory Canyon; “Eldora to Baltimore” (Rydberg). 
Populus tremuloides Michx. QuUAKING ASPEN 
A small tree of moist slopes and gulches forming characteristic groves. 
