are dispersed early in summer. The male and female flowers are 

 distinct and are borne on separate trees. The Latin varietal name 

 of the western form, tremuloides aurea, refers to the leaves, from the 

 Latin tremulus, quaking, and aurea, for golden. 



ASPENS, POPLARS, AND COTTONWOODS (Po pulus s PP .) 



Botanically, this genus presents a bewildering and complex group 

 of plants, with a large number of hybrids and other variant forms; 

 in consequence, there is a wide divergence of opinion among bota- 

 nists as to the number and names of the species. Populus is the clas- 

 sical Latin name for these woody plants. This genus is widely dis- 

 tributed in the Northern Hemisphere, principally outside the tropics, 

 and belongs to the willow family (Salicaceae), which includes only 

 one other genus, the willows (Soli spp.). Though sometimes 

 stunted and distorted by adverse growth conditions, all the poplars 

 are true trees, with aT single main stem, usually having rather broad, 

 often more or less heart-shaped, mostly long-stalked and toothed 

 leaves, and small flowers borne in hanging clusters (catkins). With 

 the exception of the narrowleaf cottonwood (P. angustifo'Ua, syn. 

 P. fortis'sima), which has short leafstalks and narrow leaves and 

 may be mistaken for a tree willow, the western poplars and cotton- 

 woods are unlikely to be confused with other plants. The flower 

 buds of willows are covered by a single scale; those of species of 

 Populus are frequently resinous and are covered with several scales. 

 In general, differentiation between members of these two genera 

 is not difficult. 



Approximately 15 species and several varieties of Populus are 

 native to the West. Based on popular names they may be separated 

 into two groups: (1) Aspens; and (2) poplars and cotton woods. 

 Poplars and cottonwoods are typical of moist sites and occur mainly 

 along streams, around ponds, and in depressions, where there is 

 plenty of subsurface moisture. They are all palatable to both live- 

 stock and game animals, being browsed whenever the foliage is 

 within reach of grazing animals. Generally, however, they are less 

 abundant and, on the whole, are of considerably less forage value 

 than aspen, although they undoubtedly furnish an appreciable 

 amount of feed. 



Narrowleaf cottonwood, next to aspen, is probably the most widely 

 distributed western species of Populus it occurs from Alberta to 

 Mexico in all the Western States except California, and is sometimes 

 associated with aspen, growing chiefly along the streams, in small 

 patches or as scattered individuals. Black cottonwood (P. tricho- 

 car'pa) is probably the most common species in the Pacific States 

 and extends to Alaska. It ranges inland to Idaho, northwestern 

 Montana, northwestern Wyoming, and Nevada. This is typically a 

 timber tree, the wood being used for apple and sugar barrels and, 

 to a limited extent, for paper pulp. The other species of Populus 

 in the West are mostly of local distribution, occurring chiefly along 

 streams at the lower altitudes; from a browse standpoint, they are 

 of limited value. 



