The Cottonwood found in the Four Corners area was for many years known as Populus fremonti, Fremont's Cottonwood, but research in the 1970s and 1980s convinced most botanists that Populus fremonti is a variety of Populus deltoides, the Eastern Cottonwood and that it is actually uncommon in the Four Corners area.  Most, but not all, botanists, now accept this classification but you will still find in older books and even in some newer books and web sites, that these two species are referred to by a variety of names: Both may be named P. deltoides.  Both may be named P. fremontii.  One may be named P. deltoides variety wislizeni and the other P. fremontii.   Or one may be named, as in this web site, P. deltoides variety wislizeni and the other P. deltoides variety fremontii.

     Populus deltoides variety fremontii, Fremont's Cottonwood, collected by John Fremont in California in 1846, is now generally accepted as the Cottonwood of California, Nevada, much of Arizona and Utah, and some of southwestern New Mexico.

     Botanists now generally agree that Populus deltoides subspecies wislizeni, the Rio Grande Cottonwood, collected by Friedrich Wislizenus in 1846-1847 on a trip from St. Louis through New Mexico and northern Mexico, is the Cottonwood of western Colorado, most of  New Mexico, far western Texas, northern Arizona, and most of eastern Utah and, thus, of almost all of the Four Corners area.  

      Both varieties are found in some areas of eastern Utah.

      The two varieties are very similar and are distinguished primarily by floral characteristics: the fruiting pedicels of P. deltoides variety wislizeni are 7-15 millimeters long versus 2-5 for variety fremontii.  The floral disk of wislizeni are 2-4 millimeters wide; those of fremontii are 4-9 millimeters wide.  Leaves of wislizeni are not as wide as, and are more pointed at the tip than, those of fremontii.

      "Populus" is Latin for "people" and is the classical Latin name for the tree.  "Deltoides" refers to the leaf shape and is from the Greek alphabet letter "delta", thus "triangular".

     A word about the ending "i" or "ii" in "wislizeni" or "wislizenii" and "fremonti" or "fremontii":  The International Code of Botanical Nomenclature several decades ago recommended dropping the double "i" at the end of botanical names.  But not everyone follows this recommendation and you will thus find varying spellings.  

     The pronunciation is also subject to controversy:  Many botanists say, "free mon tee i" but botanical Latin probably calls for the pronunciation "free mon tee" or "free mont ee".  The latter pronunciation is in accord with a common standard for the pronunciation of a botanical name that includes a person's name: pronounce it the way the person's name is pronounced.

Semi-desert, foothills. Canyons, washes, streamsides. Spring.
Hunter Canyon, Utah, May 2, 2005.

These magnificent specimens are about 50 feet tall and show all the Cottonwood features: broad, leafy canopy; dark, leaning, twisted trunks (notice the third trunk leaning out of the picture in the lower right); and canyon bottom habitat.

Friedrich Adolph Wislizenus was a St. Louis physician, friend of George Engelmann, and avid amateur botanists who made several trips to the West, including one through the Southwest into Mexico.  (More biographical information.)

Semi-desert, foothills. Canyons, washes, streamsides. Spring.
Lower Mule Canyon, Utah, April 19, 2001.

This young stand of Cottonwoods (perhaps 50 years old) has just leafed out in early spring.

Semi-desert, foothills. Canyons, washes, streamsides. Spring.
Canyonlands National Park, March 24, 2001.

Cottonwoods sometimes seem to grow in very dry, apparently hostile conditions, but a closer observation will show that their roots are tapping into water at the base of a steep hill (as in this picture) or where water is relatively near the surface because of rock formations or where washes periodically flood.

Semi-desert, foothills. Canyons, washes, streamsides. Spring.
Canyonlands National Park, March 24, 2001.

Trunks of older trees are typically gray and deeply furrowed, commonly leaning, sometimes even sprawling along the ground.  Orange tinted bark occurs occasionally.

Semi-desert, foothills. Canyons, washes, streamsides. Spring.
Dominguez Canyon, Gunnison River, May 13, 2003.

Where water is more consistent than in the dry rocky washes shown in the above two pictures, Cottonwoods grow three foot diameter trunks to about 50 feet tall with broad canopies providing shade for grasses, shrubs, and hikers (and, unfortunately, cows).