SALICACEAE 



The Poplars and Cottonwoods 

 Characteristics of the Genus Populus L. 



HABIT. Mostly large, fast-growing, deciduous trees. 



LEAVES. Alternate; simple; turning yellow before falling 

 in autumn; petioles mostly long and often laterally compressed; 

 stipules present, falling as leaves unfold. 



FLOWERS. Regular; dioecious; both sexes in drooping 

 aments; appearing from separate buds, before the leaves; indi- 

 vidual flowers solitary, apetalous, inserted on broad, cup-shaped 

 disk, subtended by dilated, lobed, and often laciniate scale or 

 bract; staminate with 4 to many stamens; pistillate, a single, 

 1 -celled, usually sessile ovary with 2-4 placentas and 2-4 stigmas. 



FRUIT. A 1 -celled, 2-4-valved capsule containing numerous 

 seeds. Seed : small, tufted with long silky hairs, extremely buoyant; 

 vitality transient and must germinate within few days. 



TWIGS. Pith homogeneous, stellate in cross section. Winter 

 buds: terminal present, covered by several scales. 



BARK. Astringent; light-colored; deeply furrowed or smooth. 



WOOD. Light; soft; weak; diffuse-porous; not durable; 

 heartwood light brown; used for pulp, veneer, and lumber. 



SILVICAL CHARACTERS. Intolerant; fast-growing; short- 

 lived; reproduction widespread and abundant; stumps and 

 roots sprout vigorously; extensive, wide-spreading root systems. 



GENERAL. This genus contains about 35 species scattered 

 over the northern Hemisphere and in Northern Africa; 9 species 

 and several hybrids are native to North America, and 2 European 

 species have become naturalized. 



KEY TO THE SPECIES OF POPLARS AND 

 COTTONWOODS 



1. Twigs, buds, petioles, and lower surfaces of leaves white tomentose; 

 widely planted and naturalized. 



2. Leaves irregularly sinuate-dentate or palmately 3-5 lobed, base 

 usually rounded or flat P. alba, White Poplar, p. 123. 



2. Leaves toothed, not lobed, base heart-shaped 



P. canescens, Gray Poplar, p. 123 



1 . Twigs, buds, petioles, and leaves hairy or glabrous at maturity. 



3. Leaf petiole round in cross section, leaf base round or heart-shaped. 

 4. Leaves broadly ovate, 4-7 inches long and nearly as broad, 



densely hairy when they unfold, but becoming glabrous; 



Atlantic Coast, southeastern and central states 



P. heterophylla. Swamp Cottonwood, p. 125. 



4. Leaves ovate to lanceolate, ^ or more longer than broad. 



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