Mention "Poplar" and some imagine a sweep of narrow, tall Lombardy Poplars lining a country road. The majestic cottonwoods of the prairie with their rounded, spreading, crowns appear rather different. Every June in eastern and western North America, it is common to see their cottony seeds drifting in the breeze. Cottonwoods, aspens and poplars are all a part of the genus Populus.
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Types of Cottonwoods
All cottonwoods are native to North America. Cottonwood is the state tree of Kansas and Wyoming. The Eastern Cottonwood (Populus deltoids) dominates eastern North America, stretching from New Hampshire to the Dakotas and south down to Texas and northern Florida. Swamp Cottonwood (P. heterophllya) grows through the southeast. Narrowleaf Cottonwood (P. angustifolia) grows in the Rockies, while Fremont Cottonwood (P. fremontii) and Black Cottonwood (P. trichocarpa) grow throughout the west.
Poplars grow mainly in the Northern Hemisphere. Relatives of cottonwood include the White Poplar, Black Poplar, European Aspen and Chinese Necklace Poplar of Europe and Asia, and the Balsam Poplar, Bigtooth Aspen and Quaking Aspen of North America.
Leaves, Flowers and Fruit: Cottonwoods
Cottonwoods are easily identifiable by their glossy-green leaves that glint in the sun when rustled by the breeze. Cottonwood leaves are typically triangular with toothed and rounded edges, but the Narrowleaf Cottonwood has lance-like leaves. Cottonwoods are named for the cottony seeds the females send off. The seeds may be messy but are harmless; male cottonwood pollen in March can trigger allergies during hay-fever season.
Leaves, Flowers and Fruit: The Poplar Family
All poplar family species have simple alternate, glossy-green leaves with rounded and toothed edges that turn golden in fall. The leafstalks are long; some have flattened leafstalks that cause the leaves to quake in the slightest breeze. Elongated buds tip the branches. The fox tail-like catkin flowers usually grow separately on male and female trees, but Lombardy poplars are grown from male clones. The fruits are small brown capsules with downy seeds.
Bark and Growth Habit
Cottonwood bark is smooth when young, but becomes thick and ridged with age. Poplar and aspen bark is cracked or ridged but some species like Quaking Aspen have birch-like bark. Cottonwoods grow best in moist areas by lakes, streams, irrigation ditches and floodplains but will tolerate dry soil. Poplars are widespread through their range and often form groves in barren, burned, or cleared areas. All are typically fast-growing, soft-wooded, short-lived trees. A cottonwood can shoot upwards to be over 100 feet high but only lives 70 to 100 years. As they age, their thick limbs are prone to wood decay and can break during harsh storms. Eastern Cottonwoods were one the few savanna trees to withstand prairie fires due to their thick bark and tendency to grow near water.
Numerous animals and birds eat the buds, seeds and twigs of poplar and cottonwood trees. Pioneers traveling across the prairies welcomed the sight of cottonwood groves since their presence signaled water was nearby. Some types of cottonwoods, poplars and aspens are planted for their beauty. The soft wood is also valued for paper pulp, construction work and the manufacture of cheaper furniture and shipping boxes, such as pallets.