Abstract
Introduction. Four species of Riella were discovered in a small anthropogenic temporary pond on Djerba island (southern Tunisia). Riella bialata Trab. is not only a very rare species worldwide, but also a new record for Tunisia, and R. cossoniana Trab., R. macrocarpa (P.Allorge) Puche, Segarra-Moragues, Sabovlj., M.lnfante & Heras, and R. notarisii (Mont.) are confirmed from Tunisia. Methods. Observations from fieldwork were combined with the results of spore culture to understand the presence of the species in this habitat. Key results. Significant differences in development, life strategy and ecology were hypothesised to promote the existence of the four Riella species in a small pond. Conservation issues were raised due to the anthropic origin of the habitat, emphasising the site's ecological significance and vulnerability.