• There are many male forms of Cottonwoods, which do not produce the "cotton" that is characteristic of the species. They are hybrids between Populus deltoides (Eastern Cottonwood) and P. nigra (Lombardy Black Poplar).
   
• Male cottonwoods generally grow between 3-4 feet a year, and can be subject to breakage.
   
• As well as "Carrizo", other forms include:

"Noreaster" Has thicker bark and is canker resistant.
"Siouxland" Slower growing; about 2-3 feet per year. Rust resistant. Resistant to canker in youth, but succumbs after 18 to 20 years.