The population structure of Carex dioica – a rare boggy species in Ukraine – has been studied for the first time. As a result, five types of spatial arrangement of C. dioica individuals, depending on their reproduction and living conditions, were established: scattered-diffuse, densely-diffuse, group, spotted and mosaic. Intensive vegetative propagation (often in the absence of seed reproduction) of individuals contributes to the group and spotted spatial structure of population. For low intensity of seed and vegetative reproduction, the arrangement of generative individuals turned out to be scattered-diffuse. Effective generative reproduction of a population was accompanied by a densely-diffuse distribution of individuals, and a combined type of reproduction (effective generative and vegetative) under favourable growth conditions contributes to its mosaic spatial structure.