General: Willow Family (Salicaceae). Native trees up to 15-20 m tall, single-stemmed with slender, upright branches forming a narrowly spreading crown. The bark is yellowish green to grayish brown, smooth on upper portions and furrowed into broad, flat ridges on older lower portions. Leaves are deciduous, simple, alternate, lanceolate to ovate-lanceolate, rounded at base, 5-9(-13) cm long, 1-2.5 cm wide, hairless or nearly so, the margins glandular-toothed, dark green above and slightly paler beneath, turning dull yellow in autumn, the petioles less than 15 mm long, about 1/3 as long as the blade, flattened only near the base. Flowers male (staminate) and female (pistillate), are on separate trees (the species dioecious). Each type is borne in pendent catkins, the female elongating to 6-8 cm long. Fruits are ovoid, pointed capsules 6-8 mm long, splitting to release the seeds; seeds 2-3 mm long, each with a tuft of long, white, silky hairs (“cotton”), easily blown by the wind. The common name is in reference to the slender leaves.

Variation within the species: No variants have been recognized within the species, but natural hybrids are frequent between narrow-leaf cottonwood and other species:

balsam poplar (P. balsamifera) = P. x brayshawii Boivin (Brayshaw’s poplar);

eastern cottonwood (P. deltoides) = P. x acuminata Rydb. (lanceleaf poplar);

Fremont cottonwood (P. fremontii) = P. x hinckleyana Correll.