Genetic diversity was studied in cattail populations (Typha angustifolia and T. latifolia) from areas around Chornobyl, site of a nuclear accident, and other locations in Ukraine. My overall objective was to evaluate radiation effects on genetics of Chornobyl Typha populations. Two types of genetic markers, microsatellites and sequences from non-coding DNA, were used. Typhas biology contributed to high spatial variability estimated from data for multiple reference populations, and this complicated the detection of radiation effects. Chornobyl populations of both species showed higher microsatellite variability for most diversity measures when compared to those of reference populations. Several characteristics showed positive correlations with radionuclide concentrations. Five percent of the total variance was observed between Chornobyl and reference populations of T. latifolia, but less than 1% of T. angustifolia which was the more variable species. Chornobyl populations of T. latifolia had a tendency to cluster together in the phylogeographic analysis. Isolation by distance was shown for T. latifolia but not T. angustifolia. Results for sequence data of T. latifolia were inconsistent with those of microsatellites. The amount of inter-population variation was higher (45%) than that for microsatellite loci (23%). Less than one percent of variation occurred between Chornobyl and reference populations, and Chornobyl populations did not cluster together on a dendrogram. Diversity measures were not different between Chornobyl and reference populations, and there were no significant differences in the number of haplotypes between the two groups. However, the number of unique haplotypes was significantly smaller in Chornobyl populations. The individual nucleotide differences of the Chornobyl samples correlated positively with radionuclide concentrations. Thus, genetic differences of Chornobyl populations are at least partially due to radiation. However, many other factors including geography, biology, ecology, and climate in addition to radiation contributed to genetic variability within and among Typha populations.