| Zusammenfassung: | Ephemerum cohaerensandE. rutheanumhave been found in 12 localities in the Dutch Rhine floodplain between 2004 and 2011, mainly in the eastern reach (Upper-Rhine and Waal). The first species is very rare in western and central Europe, the latter is a European endemic known from six countries only. All localities represent the Natura 2000 habitat type 3270, ‘Rivers with muddy banks withChenopodion rubrip.p. andBidentionp.p. vegetation’ comprising vegetation types with a late annual development on banks of former meanders, scour holes and sand and clay pits in forelands. The habitat requirements, life strategy and range structure in the Netherlands are discussed for both species. In several localities dominantEphemerumpopulations exist over tens of square meters year after year. This remarkable persistence is attributed to a special combination of environmental factors and species attributes: 1) an open vegetation on well-drained mineral soil with high moisture capacity and intermediate fertility, most commonly on sandy soils with clayey layers or with a top layer of sandy clay, 2) a regular inundation regime with high and prolonged flooding up to May or early June causing a nearly annual set back of the vegetation succession, 3) a unique variant of the annual shuttle species life strategy: the species germinate from the diaspore bank with large spores and tubers and develop an extensive protonema mat first; when moisture conditions are suitable, moss plants are formed during late summer which sporulate in autumn.
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