1. Buds with a single scale; floral bracts entire or merely toothed, tardily decidu- 

 ous or persistent; flowers with a ventral and sometimes a dorsal 



gland; disk none; stamens 2 to 7 or 8; capsule 2-valved 



2. Salix 



1. Populus L. Cottonwood. Alamo 



Fast-growing and often short-lived dioecious trees with soft wood, fissured bark 

 and mostly stout branches; branchlets slender or stout, terete or angled, pale-olive- 

 brown or grayish- to lustrous reddish-brown, glabrous to tomentose; buds terminal 

 and lateral, resinous or nonresinous, covered by several imbricated membranaceous 

 scales; leaves alternate, stipulate, varying in shape from deltoid to rhombic or 

 lanceolate, with the margins entire to variously crenate or serrate with the teeth 

 often glandular, rarely lobulate, often bearing glands on upper surface at junction 

 of leaf blade with petiole; petioles stout and much-abbreviated to elongate and 

 slender, more or less terete to laterally compressed, sometimes channeled on upper 

 side; stipules caducous; leaf scars deltoid to elliptic in shape, with 3 bundle scars; 

 flowers without a perianth, in pendulous stalked unisexual aments, appearing 

 before the leaves, borne singly, inserted on a shallow or cup-shaped symmetrical 

 or oblique persistent disk and subtended by a bract; bracts stipitate, mostly 

 cuneate or obovate, entire to variously lacerate or divided above, glabrous to 

 villous, caducous; stamens 6 to 60, the slender filaments free on the disk and the 

 small yellowish-red to purplish anthers ellipsoid to ovoid; ovary sessile on the 

 disk, with 2 to 4 parietal placentae; styles short, stigmas 2 to 4, divided into fili- 

 form lobes or broadly dilated and more or less irregularly erose; pistillate aments 

 mostly becoming elongated with age; fruit usually maturing before the leaves are 

 mature, a 2- to 4-valved dehiscent capsule, globose to ellipsoid-conic, pale- to 

 dark-brown; seeds abundant, minute, surrounded at the base by a tuft of long 

 silky white or tawny hairs that are directed upward parallel with and encom- 

 passing the seed. 



This is a genus of about 35 species, all native of the Northern Hemisphere in 

 both the Old World and New World. Many species are widely grown as orna- 

 mental shade and street trees, especially because of their rapid growth and ease of 

 propagation from cuttings. 



According to some historians, the Alamo of Texas fame received its name 

 from a grove of Populus that grew on the banks of the acequia, "alamo" being 

 the Spanish word for cottonwood. 



The resinous buds and aments of most species are valuable foods for game 

 birds, such as various grouse and quail, and some songbirds, and the tender some- 

 what succulent bark, twigs and foliage are eaten by hoofed browsers and rabbits. 

 The bark as well as the wood are favorite foods of beavers, porcupines and 

 muskrats. 



1. Petioles nearly terete, usually prominently channeled or somewhat flattened on 

 the upper side; leaf blades suborbicular-ovate to rhombic-ovate or 

 lanceolate, the margins mostly finely serrate or crenate-serrate (2) 



1. Petioles conspicuously laterally compressed (especially just below the leaf 



blades), rarely channeled on the upper side; leaf blades typically 

 deltoid to rhombic-ovate or suborbicular, the margins coarsely or 

 finely crenate-serrate (4) 



2(1). Leaf blades more than 3 times as long as wide, pale-green on the lower 

 surface, mostly obtuse to acute; petioles rarely more than 20 mm. 

 long 2. P. anqustifolia. 



2. Leaf blades rarely as much as twice as long as wide, not conspicuously paler 



on the lower surface, mostly acuminate; petioles usually more than 

 25 mm. long (3) 



738 



