Trees; trunk usually straight; bark furrowed or smooth, often gray or tan; pith mostly 5-angled in cross section. Terminal bud terete or angled; bud scales several, unequal. Stipules small, deciduous; petiole terete or laterally compressed; leaf blade usually ovate to deltoid-ovate. Flowering precocious; catkins pendulous. Flowers anemophilous; bracts apically lobed or laciniate, membranous, caducous; flowers with disc obliquely cupular. Male flower: stamens 4-many; filaments short, free; anthers dull red. Female flower: ovary 1-loculed; style 1, short or not; stigmas 2-4. Capsule 2-4(or 5)-valved. Seeds few to numerous, small. Cotyledons elliptic.
Trees, usually heterophyllous, usually clonal, clones formed by root shoots; branching usually monopodial [or sympodial]. Stems not spinose. Buds 3-10-scaled (resinous or not, terminal buds present [or absent]). Leaves deciduous; stipules present (caducous, usually minute, sometimes prominent on sucker shoots); petiole not glandular; (blade usually less than twice as long as wide, venation ± palmate, basal secondary veins strong, paired, except in Populus angustifolia, margins subentire or crenate, basilaminar glands 0-6). Inflorescences axillary or terminal, catkins, pendulous, sessile, unbranched, (leafless, flowering before leaves emerge); floral bract caducous, apex deeply or shallowly cut, (sometimes ciliate, usually glabrous, except pubescent abaxially in P. heterophylla); pistillate bract deciduous after flowering. Pedicels present. Flowers: perianth modified into non-nectariferous disc, (persistent, caducous in P. heterophylla), cup- or saucer-shaped; stamens 6-60(-70); filaments distinct; ovary 2-4-carpellate; ovules (1 or) 2-25 per ovary; styles distinct; stigmas 2-4, cylindrical to platelike, often rolled or convoluted, entire or 2-lobed. Fruits capsular, (2-4-valved, ovoid or spherical). Seeds: aril present. x = 19.
"Catkins drooping, appearing before the lvs, their scales toothed, lobed, fimbriate, or densely ciliate; each fl set on a cupulate, commonly oblique disk that may be homologous with the “glands” of Salix fls; stamens 5–80, on short filaments; styles 2–4-valved, trees or tall shrubs with soft, light wood, mostly ovate to deltoid, deciduous lvs, scaly, often viscid winter-buds, and elongate catkins that mature before the lvs are fully expanded in the spring. 40, widespread."
Male flowers with 4–many stamens; anthers oblong
Female flowers with style very short, 2–4-branched, each branch entire or 2–3-fid
Leaves on mature growth usually broad (juvenile foliage sometimes linear, ‘ Salix -like’)
Buds with several unequal outer scales
SELECTED REFERENCES Eckenwalder, J. E. 1977. North American cottonwoods (Populus, Salicaceae) of sections Abaso and Aigeiros. J. Arnold Arbor. 58: 193-208. Eckenwalder, J. E. 1984. Natural intersectional hybridization between North American species of Populus (Salicaceae) in sections Aigeiros and Tacamahaca. II. Taxonomy. Canad. J. Bot. 62: 325-335. Eckenwalder, J. E. 1996. Systematics and evolution of Populus. In: R. F. Stettler et al., eds. 1996. Biology of Populus and Its Implications for Management and Conservation. Ottawa. Pp. 7-32. Sudworth, G. B. 1934. Poplars, Principal Tree Willows and Walnuts of the Rocky Mountain Region. Washington. [U.S.D.A., Techn. Bull. 420.]
|[Latin populus, the people, many fanciful allusions supposed but none certain]|