Up to 1954 Ceratophyllum submersum L. was represented in the Netherlands herbaria mainly from a few localities in the neighbourhood of the coast, and in the living state it was practically unknown to Dutch botanists. As appears from an investigation since 1954, this species still occurs in several localities in the coastal area, and is fairly common in some parts of the province of Zeeland. It grows in oligohaline to mesohaline waters but not in salt ones. The only inland occurrence of the species is in South-Limburg (see „Naschrift”). On the map the localities known before 1954 are marked with a circle, those after 1954 with a dot (fig. 1).