WOOTON AND STANDLEY FLORA OF NEW MEXICO. 155 



1. POPULTJS L. Cottonwood. 



Trees with rough light-colored bark and scaly resinous buds; leaves usually long- 

 petioled, somewhat coriaceous, with prominent veins; flowers in i^enduloua aments, 

 appearing before the leaves; seeds with a cons^^icuous white coma (the "cotton"). 



Thia is the genus containing the common cottonwoods of the State and the less well 

 known aspen or "quaking asp" of the higher mountains. They are all rather short- 

 lived trees and grow in stations where the soil is at least moderately wet, preferring 

 the broad river valleys, where one species (P. wisKzeni) is almost the only tree, or 

 locations besides mountain streams or springs. The aspen is a characteristic plant 

 of the Canadian Zone. Three of the species here mentioned are used more or less 

 extensively and effectively as shade trees, and might well be used a great deal more. 

 The wood of all species is light and spongy and not valuable for posts or firewood, 

 although frequently used for these pui^poses for lack of something better. 



The silver-leaf poplar (Populus alba), the Lombardy poplar (P. italica), and the 

 Carolina poplar {P. deltoides) are cultivated in many localities in the State, and prove 

 very satisfactory, though short-lived, shade trees. Doctor Britton states that P. 7nexi- 

 cana S. Wats, occurs in New Mexico, but we have seen no material like the Mexican 

 plant. 



KEY TO THE SPECIES. 



Petioles flattened laterally; leaves broad, deltoid to rotund. 



Leaves broadly ovate to rotund, abruptly short-acuminate, 3 to 

 5 cm. long and broad, paler beneath; small tree of the 

 high mountains 1. P. aurea. 



Leaves broadly deltoid, acuminate, 5 to 8 cm. long and 6 to 

 10 cm. broad, of the same color on both surfaces; large 



tree of the lower valleys 2. P. wislizeni. 



Petioles terete, or channeled on the upper surface; leaves narrower, 

 ovate to narrowly lanceolate. 



Leaves ovate to ovate-lanceolate, 6 to 10 cm. long, 3 to 5 cm. 

 broad, rather coarsely crenate, both surfaces of the same 

 color 3. P. acuminata. 



Leaves broadly to narrowly lanceolate, 7 to 15 cm. long and 2 

 to 4 cm. wide, finely serrate with blunt teeth , much paler 

 beneath 4. P. angustifolia 



1. Populus aurea Tidestrom, Amer. Mid. Nat. 2: 35. 1911. Quaking aspen. 

 Populus tremuloides uurea Daniels, Univ. Mo. Stud. Sci. 2^: 98. 1911. 



Type locality: Vicinity of Mount Carbon, Colorado. 



Range : New Mexico and Arizona to British America. 



New Mexico: Common in all the higher mountain ranges. Canadian Zone. 



The aspen is a slender, white-barked tree found along streams and on cool slopes 

 of the mountains, or in shaded canyons, associated with firs and spmces, occasionally 

 forming pure forests covering small areas. It is the first tree to take possession of 

 burned areas, completely covering them before the conifers establish themselves. In 

 pure stands the trees are usually very close together, and, the trees being short-lived, 

 such forests soon become a dense tangle of fallen timber. The foliage is thin and 

 scanty, and notwithstanding the number of trees their shade is never dense. 



2. Populus wislizeni (S. Wats.) Sarg. Man. Trees N. Amer. 165. 1905. 



Valley cottonwood. 

 Populus fremontii wislizeni S. Wats. Amer. Joum. Sci. III. 15: 3. 1878. 

 Type locality: "From S. California to the Rio Grande." 

 Range : Colorado to western Texas and northern Mexico. 



