3(2). Pistillate disk sessile; fruit orbicular, 2-3 mm. in diameter; leaf blade sub- 

 orbicular-ovate to broadly deltoid-ovate, truncate to broadly rounded 



at the base, the margins sharply and unevenly serrate 



3. P. Hinckley ana. 



3. Pistillate disk on a pedicel 3-5 mm. long; fruit ellipsoid-ovoid, about 10 mm. 



long; leaf blade more or less rhombic, commonly rounded-cuneate 

 at base, the margins mostly crenate-serrate 1. P. acuminata. 



4(1). Leaf blades suborbicular to broadly ovate, abruptly apiculate to shortly 

 acuminate at apex, the margins finely crenate-serrate; found only 

 at high elevations in the mountains from Trans-Pecos Texas west- 

 ward 8. P. tremuloides. 



4. Leaf blades deltoid to broadly rhombic-ovate, coarsely or finely crenate- 



serrate; not confined to high elevations (5) 



5(4). Bud scales glabrous; leaf blades finely or coarsely crenate-serrate with 

 usually 10 to 20 teeth on each side 6. P. deltoides. 



5. Bud scales pubescent to puberulent or very rarely subglabrous; leaf blades 



usually coarsely crenate-serrate with mostly no more than 10 teeth 

 on each side (6) 



6(5). Trees of the Texas Trans-Pecos and along the Rio Grande, westward (7) 



6. Trees of the Texas Panhandle (Plains Country) and eastward (9) 



7(6). Capsule typically pvoid-ellipsoid to ovoid-conic, mostly 8-18 mm. long, 

 about as long as or slightly longer than the slender pedicels; disk 

 shallow, mostly 3-4 mm. in diameter 5. P. WisUzenii. 



1. Capsule typically orbicular to orbicular-ovoid, 3-8 (-12) mm. long, at least 

 twice as long as the short stout pedicel; disk cup-shaped, 5-8 mm. 

 in diameter (8) 



8(7). Leaves (at least some on same tree) typically shallowly or deeply cordate 



at base, triangular-acute at apex 



4. P. Fremontii var. Fremontii. 



8. Leaves typically broadly cuneate to rounded or truncate at base, typically 



tapering long-acuminate at apex 4. P. Fremontii var. arizonica. 



9(6). Leaf blades with a pair of glands on upper surface at juncture with 

 petioles 7. P. Sargentii var. Sargentii. 



9. Leaf blades without basal glands or rarely with rudimentary glands 



7. P. Sargentii var. texana. 



1. Populus acuminata Rydb. Lanceleaf cottonwood, smooth-barked cotton- 

 wood. Fig. 379. 

 Tree to about 18 m. tall, with a trunk 2-5 dm. in diameter, the stout branches 

 ascending and spreading to form a compact pyramidal or domelike crown; bark 

 smooth and whitish when young, with age becoming pale grayish-brown and 

 deeply fissured to form narrow flat ridges; branchlets slender, terete to somewhat 

 4-angled, pale greenish-brown, glabrous or somewhat pubescent; buds elliptic- 

 conic, sharp-pointed, curved, resinous, bright reddish-brown, subglabrous to 

 pubescent, about 1 cm. long; leaf blades firm, dark-green and shiny on the upper 

 surface, only slightly paler green on the lower surface, rhombic-lanceolate to 

 rhombic-ovate or broadly ovate, gradually or abruptly subacute to acuminate- 

 attenuate at the apex, broadly rounded to cuneate at the base, the margins usually 

 finely (or occasionally coarsely) crenate-serrate except near apex, 5-12 cm. long, 

 usually about half to two thirds as wide as long, rarely about as wide as long; 

 petiole nearly terete, usually somewhat channeled on the upper side, glabrous to 

 puberulent, 2.5-7.5 cm. long, rarely shorter; aments 5-12 cm. long; floral bracts 

 glabrous, scarious, caducous, dilated and irregularly lacerate at the apex; staminate 

 aments densely cylindric, with short pedicels and oblique disks that support 

 numerous stamens; pistillate aments more laxly flowered, with mature pedicels 



739 



