Atriplex garrettii Rydb. is a diploid, dioecious member of the Chenopodiaceae family with a known male specific genetic marker. Sex determination in this species appears to be genetically controlled with a 1:1 segregation of sexes. In harsh environments, some species exhibit a male biased sex ratio. However, A. garrettii exhibits unbiased sex ratios in its natural populations. This study assessed whether spatial segregation of sexes occurs within populations. Other studies have shown that in populations which exhibit differential spatial distribution of sexes, females prevail in resource rich microhabitats while males prevail in resource poor sites. Three populations of A. garrettii, growing in dry, sandy soils along the Colorado river near Moab, Grand County, Utah, were assessed for spatial segregation of sexes within populations. One hundred individuals per population were randomly selected using the point quarter method. Sex was recorded for all individuals and their nearest neighbors. Microenvironmental parameters (soil moisture, soil pH, etc.) were assessed for each sampled individual. Plant height and foliar crown diameter were measured to determine if males of A. garrettii are larger than females. Xylem water potential of each individual was assessed using a pressure chamber to determine if there was differential water stress in females and males. Degree of parasitism/pathogenic infection was measured for all individuals and compared between sexes.

Key words: Atriplex garettii, dioecy, resource allocation, sex ratio, sexual dimorphism, water stress