Populus

Populus
Foliage of Populus tremula
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Malpighiales
Family:	Salicaceae
Tribe:	Saliceae
Genus:	Populus
Type species
Populus tremula

Male catkins of Populus × canadensis

Populus is a genus of trees common in the northern hemisphere. They are often called just poplars. The genus has 25–35 species in three sub-groups, which are called poplars, aspens, and cottonwoods.

In the September 2006 issue of Science, it was announced that the Western Balsam Poplar (P. trichocarpa) was the first tree to have its full DNA code sequenced.

Reproduction

The flowers are mostly dioecious (rarely monoecious) and appear in early spring before the leaves. They are borne in long, drooping catkins. The male flowers have a group of 4–60 stamens on a disk. The female flower is a single-celled ovary in a cup-shaped disk.

Pollination is by wind. The fruit is a two to four-valved capsule, green to reddish-brown, mature in mid summer. It contains tiny light brown seeds surrounded by tufts of long, soft, white hairs which help wind dispersal.

Ecology

Poplars of the cottonwood section are often wetlands or riparian trees. The aspens are among the most important boreal broadleaf trees.

Poplars and aspens are important food plants for the larvae of a large number of Lepidoptera species. Pleurotus populinus, the aspen oyster mushroom, is found exclusively on dead wood of Populus trees in North America.