Populus trichocarpa
A model tree species with cottony seeds and invasive roots.
Populus trichocarpa—commonly called black cottonwood, western balsam-poplar, or California poplar—is a deciduous broadleaf tree native to western North America. It is grown for timber and is also a model organism in plant biology. Each spring, the tree releases cottony fluff that carries its seeds.
This species can reach 30 to 50 meters tall, with trunks over 2 meters in diameter. Among poplar species, it ranks third in the American Forests Champion Tree Registry. Though usually short-lived, some individuals survive up to 400 years. The national and world record holder, a black cottonwood in Willamette Mission State Park near Salem, Oregon, measured 47 meters tall and 8.8 meters around in April 2008, earning 527 points.
The bark is gray and covered with lenticels, becoming thick and deeply fissured on older trees; it can harden enough to spark when cut with a chainsaw. Older stems are gray, while younger ones are light brown. The crown is typically conical and dense, with lower branches drooping on large trees. Spur shoots are common, and the wood is light-colored with a straight grain.
Leaves are usually 7 to 20 centimeters long, glossy dark green above and glaucous light gray-green below. Larger leaves, up to 30 centimeters, may appear on stump sprouts or vigorous young trees. They are alternate, elliptical with crenate margins and acute tips, and have reticulate venation. The petiole is reddish. Buds are conical, long, narrow, and sticky, emitting a strong balsam scent when they open in spring.
The root system is extensive and aggressive, capable of invading and damaging drainage systems and, by drying out soil, even undermining building foundations. In 2016, direct evidence showed that wild P. trichocarpa fixes nitrogen.
The species is normally dioecious, with male and female catkins on separate trees. Flowering begins around age 10. In Washington and Oregon, flowers appear from early March to late May; in northern and interior British Columbia, Idaho, and Montana, they may appear as late as mid-June. Staminate catkins have 30 to 60 stamens, are 2 to 3 centimeters long, and are deciduous. Their pollen can be an allergen. Pistillate catkins mature to 8 to 20 centimeters long, bearing rotund-ovate, tricarpellate, subsessile fruits 5 to 8 millimeters long. Each capsule contains many tiny seeds with long, white, cottony hairs.
Seeds ripen and disperse
- Height
- 30 to 50 m (98 to 164 ft)
- Trunk diameter
- over 2 m (6+1⁄2 ft)
- Lifespan
- normally short-lived, but some up to 400 years
- Flowering age
- around 10 years
- Native range
- western North America from Alaska to Baja California
- Conservation status
- rated secure (T5) by NatureServe as a subspecies of Populus balsamifera
Lore & Background
Populus trichocarpa is a large tree, growing 30 to 50 m tall with a trunk diameter over 2 m. It ranks third in poplar species in the American Forests Champion Tree Registry. A specimen in Willamette Mission State Park near Salem, Oregon, holds national and world records, measured in April 2008 at 47 m tall and 8.8 m around. The bark is grey with lenticels, becoming thick and fissured on old trees, hard enough to cause sparks when cut with a chainsaw. Leaves are 7–20 cm long, glossy dark green above and glaucous grey-green below, with a reddish petiole. The buds are conical, sticky, and have a strong balsam scent in spring. The tree has an extensive root system that can damage drainage systems and building foundations. In 2016, the first direct evidence was published indicating that wild P. trichocarpa fixes nitrogen.
Reader's Guide
Populus trichocarpa is significant as a model organism in plant biology, providing insights into tree genetics, growth, and adaptation. Its rapid growth and ability to colonize disturbed sites make it a pioneer species in riparian habitats across western North America. The tree's cottony seeds are dispersed by wind and water, enabling it to establish on bare, moist seedbeds after floods or logging. It hybridizes with three other poplar species in the region, contributing to ecological diversity. Ecologically, it supports wildlife: woodpeckers create cavities used by various animals, larger birds nest in its branches, and beavers use it for food and dam-building. Its wood is used for timber, and the fragrant buds yield extracts for cosmetics. Native American tribes utilized its bark, sap, wood, and roots for medicinal and practical purposes, including fire-making, canoe building, and glue. The species has been successfully introduced to the Faroe Islands and Iceland, where it has become widespread. Its invasive roots and susceptibility to rot and splitting pose challenges in cultivation, but its fast growth and scented spring foliage make it a valued ornamental.
Did You Know?
- The tree's bark can become hard enough to cause sparks when cut with a chainsaw.
- In 2016, the first direct evidence was published indicating that wild P. trichocarpa fixes nitrogen.
- The species was imported from Alaska to Iceland in 1944 and has since become one of the most widespread trees there.
- The tree has the ability to abscise shoots complete with green leaves, which may root and colonize exposed sandbars.
More in Flowering Trees & Shrubs 1-20
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record