The species-rich genus Carex (Cyperaceae) is one of the 7% of angiosperm genera containing dioecious species. Dioecy is rare in Carex, only 12 spp. out of the 1,776 recorded taxa having been identified as dioecious. This paper focuses on Carex davalliana and C. dioica, the two dioecious species recorded in Europe. We investigated the nuclear (ITS) and chloroplast (trnTLF, rpl16) phylogenies of European Carex and identified incongruence in the phylogenetic history of both C. davalliana and C. dioica. This incongruence probably resulted from hybridisation. We postulate that dioecism was generated from hybridisation between species of opposite inflorescence morphologies (androgynous vs. gynaecandrous). We discuss the advantages of the separation of genders, taking into account the low number of dioecious species in the genus.