The Cottonwood found in the Four Corners area was for many years known as Populus fremontii, Fremont's Cottonwood, but research in the 1970s and 1980s convinced most botanists that Populus fremontii is a subspecies of Populus deltoides, the Eastern Cottonwood and that it is actually uncommon in the Four Corners area. The Four Corners area Cottonwood is now generally accepted as Populus deltoides subspecies wislizeni. 

      Populus deltoides subspecies 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.

    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.

     The names for these plants on this web site follows the Synthesis, The Flora of North America, and Weber's Colorado Flora (2012).

      The two subspecies are very similar and are distinguished primarily by floral characteristics: the fruiting pedicels of P. deltoides subspecies wislizeni are 7-15 millimeters long versus 2- 5 mm for subspecies fremontii.  The floral disk of wislizeni are 2-4 mm wide; those of fremontii. are 4-9 mm 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"and "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.  There also seems to be some disagreement about whether the International Code really did recommend dropping the "ii"! The Synthesis and The Flora of North America spell one subspecies, "fremontii", but the other "wislizeni".

     The pronunciation of "fremonti(i)" is also subject to controversy:  Many botanists say, "free mon tee i" but botanical Latin probably calls for the pronunciation "free mont e".  The latter pronunciation is in accord with a standard for pronouncing botanical names that includes a person's name: pronounce the person's name as they would have pronounced it and then add the ending. The Latin "i" is pronounced "e".

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.
Canyonlands National Park, October 28, 2009.

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

Cottonwoods sometimes seem to grow in very dry conditions, apparently hostile for them, 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.  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 wash shown in the above picture, Cottonwoods grow three foot diameter trunks (as shown here) to about 50 feet tall with broad canopies providing shade for grasses, shrubs, and hikers (and, unfortunately, cows).

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Populus deltoides  

Range map for Populus deltoides subspecies fremontii

Range map for Populus deltoides subspecies wislizeni