Editing Populus (section)

==Description==
[[File:Trembling Aspen.jpg|thumb|Mature trembling aspen trees (''Populus tremuloides'') with young regeneration in foreground, in Fairbanks, Alaska]]
The genus has a large genetic diversity, and can grow from {{convert|15|-|50|m|abbr=on}} tall, with trunks up to {{convert|2.5|m|ft|abbr=on|frac=2}} in diameter.

[[File:Populier mannelijke bloeiwijze (Populus canadensis male inflorescences).jpg|left|thumb|upright|Male catkins of [[Populus × canadensis|''Populus'' × ''canadensis'']]]]
The [[Bark (botany)|bark]] on young trees is smooth and white to greenish or dark gray, and often has conspicuous [[lenticel]]s; on old trees, it remains smooth in some species, but becomes rough and deeply fissured in others. The shoots are stout, with (unlike in the related [[willow]]s) the terminal bud present. The [[leaves]] are spirally arranged, and vary in shape from triangular to circular or (rarely) lobed, and with a long [[petiole (botany)|petiole]]; in species in the sections ''Populus'' and ''Aigeiros'', the petioles are laterally flattened, so that breezes easily cause the leaves to wobble back and forth, giving the whole tree a "twinkling" appearance in a breeze. Leaf size is very variable even on a single tree, typically with small leaves on side shoots, and very large leaves on strong-growing lead shoots. The leaves often turn bright gold to yellow before they fall during autumn.<ref name=rdm>Meikle, R. D. (1984). ''Willows and Poplars of Great Britain and Ireland''. BSBI Handbook No. 4. {{ISBN|0-901158-07-0}}.</ref><ref name=rushforth>Rushforth, K. (1999). ''Trees of Britain and rope''. Collins {{ISBN|0-00-220013-9}}.</ref>

[[File:Populus (Populier zaadpluis en zaden)1.jpg|thumb|right|The seeds of the poplar tree are easily dispersed by the wind, due to the fine hairs surrounding them.]]
The [[flower]]s are mostly [[dioecious]] (rarely [[monoecious]]) and appear in early spring before the leaves. They are borne in long, drooping, sessile or pedunculate [[catkin]]s produced from buds formed in the axils of the leaves from the previous year. The flowers are each seated in a cup-shaped disk which is borne on the base of a scale which is itself attached to the rachis of the catkin. The scales are obovate, lobed, and fringed, membranous, hairy or smooth, and usually caducous. The male flowers are without [[calyx (botany)|calyx]] or [[Corolla (flower)|corolla]], and comprise a group of four to 60 [[stamen]]s inserted on a disk; filaments are short and pale yellow; [[anther]]s are oblong, purple or red, introrse, and two-celled; the cells open longitudinally. The female flower also has no calyx or corolla, and comprises a single-celled ovary seated in a cup-shaped disk. The style is short, with two to four stigmata, variously lobed, and numerous ovules. Pollination is by wind, with the female catkins lengthening considerably between pollination and maturity. The [[fruit]] is a two- to four-valved [[dehiscence (botany)|dehiscent]] [[capsule (fruit)|capsule]], green to reddish-brown, mature in midsummer, containing numerous minute, light-brown [[seed]]s surrounded by tufts of long, soft, white hairs aiding wind dispersal.<ref name=rdm/><ref name=Keeler>{{cite book |last=Keeler |first=H. L. |title=Our Native Trees and How to Identify Them |publisher=Charles Scribner's Sons |year=1900 |location=New York |pages=410–412}}</ref>