Populus
A genus of poplars, aspens, and cottonwoods with wind-pollinated catkins.
Populus is a genus of more than 60 species of deciduous flowering plants belonging to the willow family, Salicaceae. These trees are native to temperate, subarctic, and mountain regions across Eurasia, North America, and North Africa, as well as the tropical highlands of East Africa. Depending on the species, they are commonly called poplar, aspen, or cottonwood. In 2006, the western balsam poplar (Populus trichocarpa) became the first tree to have its entire genome sequenced.
Members of this genus vary greatly in size, reaching heights of 15 to 50 meters (49–164 feet), with trunks up to 2.5 meters (8 feet) in diameter. Young trees have smooth bark that is white, greenish, or dark grey, often marked with conspicuous lenticels; on older trees, the bark may remain smooth in some species or become rough and deeply fissured in others. The shoots are stout and, unlike those of related willows, always have a terminal bud. Leaves are arranged spirally and come in shapes ranging from triangular to circular, rarely lobed, with long petioles. In species from the sections Populus and Aigeiros, the petioles are flattened sideways, causing the leaves to flutter easily in a breeze and giving the tree a twinkling appearance. Leaf size varies widely even on a single tree, with small leaves on side shoots and much larger leaves on vigorous leading shoots. In autumn, the leaves often turn bright gold or yellow before falling.
The flowers are mostly dioecious (rarely monoecious) and appear in early spring before the leaves. They grow in long, drooping catkins, either stalkless or stalked, from buds formed the previous year
- species_count
- over 60 accepted species
- height_range
- 15–50 m (49–164 ft) tall
- trunk_diameter
- up to 2.5 m (8 ft)
- leaf_type
- deciduous, spirally arranged
- pollination
- wind
- first_sequenced_tree
- Populus trichocarpa (2006)
- oldest_fossil_genus
- Populus wilmattae, Late Paleocene (~58 million years ago)
Lore & Background
Populus species are dioecious (rarely monoecious), with flowers appearing in early spring before leaves, borne in long, drooping catkins. Male flowers have 4 to 60 stamens; female flowers have a single-celled ovary. The fruit is a dehiscent capsule containing numerous seeds with white hairs aiding wind dispersal. The bark is smooth on young trees, becoming rough and fissured in some older trees. Leaves vary from triangular to circular, with laterally flattened petioles in some sections that cause a twinkling motion in breezes.
Reader's Guide
Populus is ecologically and economically significant. Aspens are among the most important boreal broadleaf trees, and cottonwood poplars are often wetland or riparian trees. The genus is a key food source for many Lepidoptera larvae. In cultivation, poplars are grown as ornamentals and for plywood, notably in India's Punjab region. They grow rapidly and can form large clonal colonies, such as the Pando forest of Populus tremuloides clones. However, their invasive root systems can damage foundations and pipes. Hybridization is common, and genetic studies have revealed reticulate evolution due to past hybridization and introgression.
Did You Know?
- The western balsam poplar (P. trichocarpa) was the first tree to have its full DNA code sequenced, in 2006.
- The oldest easily identifiable fossils of the genus are Populus wilmattae from the Late Paleocene of North America, about 58 million years ago.
- Poplars can grow from cuttings or broken branches, and some species form huge clonal colonies like the Pando forest of Populus tremuloides.
- The aspen oyster mushroom (Pleurotus populinus) is found exclusively on dead wood of Populus trees in North America.
More in Flowering Trees & Shrubs 1-20
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