The Rio Grande Cottonwood, a welcome sight to pioneer desert caravans because it often signaled water, typically reaches 50 to 60 feet in height, with a trunk of three feet in diameter. Some of the grand old cottonwoods in the Rio Grande Valley have reached 90 feet in height, with trunks five feet across. In open areas, the tree may divide into branches near its base, producing a spreading crown. . . .
The Rio Grande Cottonwood reproduces by seeding, unlike many other flood-plain trees which regenerate by sprouting. It flowers in the spring, before it leafs out. It releases its seeds, each carried by downy white tuft, or “parachute,” in anticipation of traditional spring floods and winds, the principal mechanisms for dispersion. A mature Rio Grande Cottonwood can produce as many as 25 million seeds in a season, covering wide areas with a blanket of “cotton.”
And the seedlings can grow roots at the rate of 3-5 feet in a summer to keep up with a falling water level as the floods subside.