Description from Flora of China
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.
About 100 species: N Africa, Asia, Europe, North America; 71 species (47 endemic) in China, including at least nine hybrids.
The taxonomy of Populus in China, at species level, is at a preliminary stage. To reach an adequate understanding, it is necessary to make direct observations in natural populations of all morphological variations between individuals, for all species and at all seasonal developmental stages. Moreover, other methods beyond morphological studies need to be applied, especially anatomic and chemotaxonomic analyses.