Appearance''P. fremontii'' is a large tree growing from 12–35 m in height with a wide crown, with a trunk up to 1.5 metres in diameter. The bark is smooth when young, becoming deeply fissured with whitish cracked bark on old trees.
The 3–7 centimetres long leaves, are cordate with an elongate tip, with white veins and coarse crenate teeth along the sides, glabrous to hairy, and often stained with milky resin. Autumn colors occur from October–November, mainly a bright yellow, also orange, rarely red.
The inflorescence consists of a long drooping catkin, which blooms from March to April. The fruit is a wind dispersed achene, that appears to look like patches of cotton hanging from limbs, thus the name cottonwood.
NamingTwo subspecies are currently recognized. Some confusion due to hybridization with a Rio Grande subspecies of ''Populus deltoides'' subsp. ''wislizeni'' had originally placed this eastern cottonwood subspecies as a ''P. fremontii'' subspecies, but it was removed in 1977.
⤷ ''P. f.'' subsp. ''fremontii'', with synonyms ''P. f.'' var. ''arizonica'' - Sarg. and ''P. f. ''var.'' macdougalii'' - Jeps. from California and west of the Continental Divide
⤷ ''P. f.'' subsp. ''mesetae'' - Eckenwal., of arid areas of Mexico and west Texas, and widely planted elsewhere, generally east of the Continental Divide
DistributionThe tree is native to the Southwestern United States and Mexico. In the United States, the species can be found in California, Idaho, Nevada, Utah, Arizona, New Mexico, Texas, and Colorado. In Mexico, it can be found in Baja California, Baja California Sur, Sonora, Chihuahua, Coahuila, Nuevo León, México , and Puebla.
HabitatThe riparian tree grows near streams, rivers, springs, seeps, wetlands, and well-watered alluvial bottomlands at elevations below 2,000 metres elevation.
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