Abstract

Atriplex is a genus in the Chenopodiaceae, the perennial members of which are ecologically important in western North America. Seventeen species and one subspecies of perennial Atriplex occur in Utah and the northern deserts. Three of these species and the subspecies were described by the writer in a recent publication as a result of extensive field work leading to this study. These are A. welshii, A. navajoensis, A. bonnevillensis, and A. cuneata ssp. introgressa. This study is an investigation of the systematics and phytogeography of the perennial Atriplex in Utah and the northern deserts, with emphasis on the A. gardneri and A. garrettii groups. Since the publication of the Phylogenetic Method in Taxonomy (Hall and Clements, 1923) little systematic work has been done on North American Atriplex. The results of this study indicate that considerable reorganization of taxa occurring within the northern deserts is necessary. The five species formerly classified within A. "nuttallii" Wats. are considered specifically distinct because they are not only discrete morphologically, but soil analysis indicate they have differing edaphic requirements and do not interbreed when sympatric. Nine hybrids are fully discussed. Of these, only one was previously recognized as a hybrid. In addition, one species (A. bonnevillensis) and the subspecies (A. cuneata ssp. introgressa) were found to be of hybrid origin. Scatter diagram analyses are included for six of these hybrids and their parents and the two taxa of hybrid origin. Each taxon is thoroughly described and collection sites are given. Almost all the northern desert species and their hybrids are figured with photographs, and the newly described species and members of the A. "nyttallii" group are figured with line drawings. As the fruiting bract appears to have the most useful diagnostic value, these are illustrated for all northern desert species and hybrids. An attempt has been made to put the nomenclature in order and all synonyms are given. The epithet A. "nuttallii" Wets. is invalid because it is antedated by A. gardneri (Moq.) Dietr .

Degree

College and Department

Life Sciences; Plant and Wildlife Sciences

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