Our purpose is to discuss the impact of alien plants on rangeland ecosystems of the Great Basin in terms of their effects on biological functions. The sagebrush/bunchgrass ranges of western North America are used as a model ecosystem for the impact of alien plants. Alien weed species have been introduced in successive waves, with the success of each new introduction dependent on how well adapted to the environment and how competitive the new weed is with those previously introduced. Annual species have been successful across extensive areas of Great Basin rangelands. Biennial and short- and long-lived perennial introductions have been restricted to much more specific habitats. Alien plants impact rangelands through stand renewal and successional processes. Alien weeds can cause such processes to be accelerated and/or truncated depending on the species and range site.
Descriptions, illustrations, and distribution data are given for four annual species of Chenopodiaceae native to western North America: Atriplex argentea Nutt., A. truncata (Torrey) Gray, A. powellii Watson, and A. dioica (Nutt.) Macbr. All four species have the same chromosome number, 2n = 18. Scanning electron photomicrographs of the pollen grains are included.
