Riccia fluitans and R. rhenana are widely distributed aquatic liverworts with challenging species delimitation. The insufficient identification causes uncertainty in the species distribution. In this study, we summarize the occurrence data for Bulgaria, and compare it with the records available in GBIF database for the territory of Europe. Based on the Bulgarian occurrence and the European occurrence, comparison of the frequencies of both species is made. The results of the detailed studies of Riccia fluitans complex in Bulgaria show the opposite pattern as compared to the European occurrence in GBIF. This is a consequence of hard morphological delimitation between the two taxa, which are cytogenetically clearly distinctive. The striking prevalence of R. fluitans over R. rhenana from GBIF data shows the need for careful species determination and highlights the risks of using such databases. The field data from Bulgaria indicated species-specific trends with respect to habitat origin and microhabitat preferences.
Gospodinov et al. (Thu,) studied this question.