Hordeum jubatum and Parentucellia viscosa have been found in the Netherlands since the beginning of this century. However they do not belong to the Standardlist of the Netherlands flora. Both species have settled on sandy flats in the recently closed estuaries (Grevelingen, Veerse Meer) in the South-west Netherlands. It is not clear if this occurred spontaneously or was induced by man. However it is certain, that the species have been able to maintain themselves in this area for almost ten years and colonize new places as well. Hordeum jubatum is found mainly in open vegetation on desalinating soils. This vegetation belongs mainly to mixtures of the alliance Agropyro-Rumicion crispi and halophytes. There are clear indications that H.jubatum is not always an annual. In 1979 in the Grevelingen area the roots of dead parts remaining from the summer formed vegetative shoots that autumn. Parentucellia viscosa grows mainly in vegetation belonging to mixtures of the alliance Nanocyperion flavescentis and grassland communities of Agropyro-Rumicion crispi.