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Genetic diversity studies of wetland plants are scarce, but estimates of genetic diversity are useful for learning about plant biology or developing appropriate management strategies. We used allozymes to examine patterns of genetic diversity in Cladium jamaicense, the dominant plant species of the Florida Everglades. We sampled 18 populations (a total of 818 plants) in a replicated grid pattern. Because C. jamaicense can reproduce asexually, we compared estimates of genetic diversity calculated using all sampled ramets to those using only genets within populations. Fewer than half of the 13 loci studied were polymorphic (P. = 46.2%), with just under two alleles per locus on average (A. = 1.9). Heterozygosity was also low and was lower for ramet-level estimates (ramets: H[sub es] = 0.069, H[sub ep] = 0.051; genets: H[sub es] = 0.094, H[sub ep] = 0.067). Ramet-level estimates indicated heterozygote excess in eight populations and heterozygote deficiencies in four populations, but genet-level estimates indicated inbreeding in only one population. Ramet-level estimates indicated significant population differentiation (F*[This character cannot be converted to ASCII text] = 0.268), but genet-level estimates did not (F*[This character cannot be converted to ASCII text] = 0.035). Similarly, mean genetic distance between populations was higher based on ramet-level estimates (D = 0.024) than genet-level estimates (D = 0.016), and we found a weak correlation between genetic and geographic distance based on ramet-level estimates (r = 0.15, P = 0.02) but not genet-level estimates (r = 0.04, P = 0.2). Thus, clonal reproduction resulted in effective genetic differentiation among populations. Observed patterns of population differentiation may reflect high levels of gene flow among populations or patterns established during colonization that persist through long-lived clones. Genetic diversity of Everglades C. jamaicense was low compared to other sedges or other species ... [ABSTRACT FROM AUTHOR]