New habitats opened up in western North America since the recession of Lake Bonneville and Lake Lahontan have admitted a host of new species of Atriplex. Every known evolutionary force is operating and at accelerated paces. Autoploidy appears to be more common than in any other reported group of plants. Natural hybridization between closely related species has provided a wealth of fertile segregants from which new adaptive types have been and are being selected. Hybrids between more distantly related species are sterile and some appear to have given rise to fertile alloploid derivatives.
All evidence points to a center of origin for Atriplex in northern Mexico. The numerous species which have migrated northward into western United States and Canada were apparently able to do so because attributes acquired to make them adaptive in the hot dry deserts of Mexico were characteristics which, uniquely, also pre-adapted them for colder climates and alkaline clay soils to the north. Woody species such as Atriplex canescens and A. confertifolia hybridize rather easily with herbaceous perennial species such as A. cuneata, A. gardneri, A. corrugata, and A. obovata. Since most such hybrids are at least partly fertile and produce F2 segregants of both woody and nonwoody types, the genetic basis for the accumulation of wood is apparently rather simple.
Stutz, Howard C.
"Explosive evolution of perennial Atriplex in western America,"
Great Basin Naturalist Memoirs: Vol. 2
, Article 10.
Available at: http://scholarsarchive.byu.edu/gbnm/vol2/iss1/10