The small (to 7 cm. long) suborbicular-ovate to broadly deltoid-ovate leaf 

 blades and much-abbreviated pistillate aments, with their sessile floral disks, are 

 characteristics that distinguish this species from the allied P. angustifolia and 

 P. acuminata. 



4. Populus Fremontii Wats. Fig. 382 (var. arizonica). 



Tree to about 30 m. tall, with a thick often short trunk to 1 m. or more in 

 diameter, the branches large and ascending or wide-spreading to form a broad 

 open crown; bark pale-gray or whitish, thick, in age pale-greenish and deeply 

 fissured to form broad plates; branchlets (and sometimes older wood) noticeably 

 pubescent to glabrous, rather slender, at first pale-green, later tan-color to yellow- 

 ish or grayish; buds ovoid, only slightly resinous, pale-orange-brown, densely 

 hirsute, 1-2 cm. long; leaf blades leathery, glabrous to more or less pubescent or 

 puberulent, yellowish-green and lustrous on the upper surface, paler on the lower 

 surface, broadly deltoid to rhombic-ovate or triangular-ovate, abruptly acute- 

 apiculate to long-acuminate at the usually entire apex, truncate to rounded or 

 broadly cuneate to shallowly or deeply cordate at the base, the margins with few 

 to many coarse glandular-crenate teeth, very rarely with poorly developed glands 

 at juncture with petioles, 5-14 cm. long, mostly about as wide as long; petioles 

 slender, mostly somewhat pubescent, laterally compressed (especially just below 

 the leaf blade), sometimes channeled on the upper side, 2.5-9 cm. long; aments 

 6-10 cm. long; floral bracts caducous, scarious, narrowly cuneate, lacerate on the 

 apical margin, about 2 mm. long; staminate aments densely cylindric, with pedicels 

 about 1 cm. long and disks to 1 cm. in diameter, the disks supporting 20 to 30 

 (-60) stamens with anthers about 2 mm. long; pistillate aments more laxly 

 flowered, with mature stout pedicels 1-3 (rarely more) mm. long and the large 

 disks cup-shaped and 5-8 mm. in diameter; stigma lobes broad, flattened, crenate; 

 fruits orbicular to orbicular-ovoid, deeply pitted, 3-8 (-12) mm. long, 3- to 

 4-valved; seeds ellipsoid, apiculate, compressed, 2-2.5 mm. long. 



Along streams, in swamps and wettish bottomlands, about springs and water 

 tanks. Calif, and Nev., through Ariz., N.M. and (as var. arizonica) to w. Tex., 

 Feb. -Apr.; also n. Mex. 



Our two variants are distinguished in the key. It is quite possible that the 

 Arizona Cottonwood or chopo, var. arizonica (Sarg.) Jeps. {P. arizonica Sarg.), 

 should be referred to var. pubescens Sarg. 



5. Populus Wislizenii (Wats.) Sarg. Rio Grande cottonwood, alamillo. 



Fig. 383. 



Tree 8-25 m. tall, with a thick trunk to about 1.5 m. in diameter, the branches 

 large and wide-spreading to form a broad somewhat flat-topped open crown; bark 

 pale-grayish-brown, thick, deeply fissured to form broad flat plates; branchlets 

 rather stout, glabrous, yellowish or light-yellowish-brown; buds ellipsoid-conic, 

 sharp-pointed, somewhat resinous reddish-brown or greenish and brown, puber- 

 ulous to densely hirsute, 1.5-2 cm. long; leaf blades coriaceous, yellowish-green 

 and more or less shiny on both surfaces, turning bright-yellow in autumn, broadly 

 deltoid to deltoid-ovate, rather abruptly triangular-acuminate (rarely attenuate) 

 at the entire apex, cordate to truncate at the base, the margins coarsely crenate- 

 serrate with usually less than 10 glandular teeth on each side, eglandular at base, 

 5-14 cm. long, usually as broad as or broader than long; petioles slender, laterally 

 compressed, 3-10 cm. long; aments 8-15 (usually about 10) cm. long; floral 

 bracts caducous, obovate, lacerate on the apical margin, about 2 mm. long; 

 staminate aments densely cylindric, with pedicels 4-8 mm. long and oblique disks 

 about 3 mm. in diameter, the disks supporting numerous stamens with reddish 

 anthers 1-1.5 mm. long; pistillate aments more laxly flowered, with mature pedi- 



745 



