Recent decades have witnessed growing interests in exploring the population genetics and phylogeography of crop plants and their wild relatives because of their important value as genetic resources. In this study, sequence variation of the nuclear Adh1a gene was used to investigate the genetic diversity and phylogeographic pattern of the wild and cultivated Zizania latifolia Turcz. Sequence data were obtained from 126 individuals representing 21 wild populations in China and 65 varieties of the cultivated Zizania latifolia. Low to medium level nucleotide diversity was found in the wild populations, with northeastern populations being the most variable. We detected significant population subdivision (F-ST = 0.481) but no significant phylogeogaphical structure, suggesting limited gene flow and dispersal among populations. The current pattern of genetic variation in the wild populations might be explained by a fragmentation of ancient populations due to habitat destruction and degradation during recent decades. The heterogeneous levels and spatial apportionment of genetic diversity among wild populations also suggested a history of gradual colonization of Zizania latifolia populations from the northeast to the south of China. Interestingly, all 65 varieties of the cultivated Zizania latifolia possessed a single identical genotype, implying a single domestication associated with very few initial individuals.