Abstract: | Abstract Ephemerum hibernicum sp. nov. is described from inundation zones of two lakes and a river in north-central Ireland and a river in western Ireland. It is most similar to E. crassinervium and E. sessile, but differs from both of these in several characters of the leaves. In particular, papillae on the upper lamina are much lower than in most E. crassinervium, while the leaves are longer and wider than in E. sessile, with a wider lamina towards the leaf apex, less well-defined costa and sometimes with large spinose marginal teeth. Ephemerum hibernicum is a rare species and its specialized habitat merits conservation. |