The discovery in 1962 of a single specimen of Polygonum maritimum L. on drift material washed ashore at the north coast of the isle of Noord-Beveland gives rise to a discussion of its taxonomical, geographical and ecological characteristics. The species has never been found in the Netherlands before. An enumeration of the taxonomical features of P. maritimum and a comparison with those of P. aviculare L. agg. and of the allied taxa P. raii Babingt. and P. oxyspermum Mey. & Bge. is given. The mediterranean-atlantic species P. maritimum reaches its north-eastern limit on the continent in the French counties Manche and Calvados, in England in the counties Somerset and Hampshire. Thus the locality in the Netherlands is situated about 400 km north-east of this limit. It must be accepted that diaspores can be transported over this distance among drift material of southern origin. In the phytocoenological system of the French-Swiss school P. maritimum is a faithful taxon of the mediterranean-atlantic alliance Euphorbion peplis growing on drift material washed ashore. However, at the european-atlantic coast the species penetrates into the Atriplicetum sabulosae, an association of the alliance Salsolo-Honckenyon peploidis which vicariates with the former alliance in northern regions. A vegetation record of the locality in Noord-Beveland is given. While discussing the ecology of P. maritimum special attention is devoted to the combination of leveling and differentiating aspects of the habitat of tidal drift belts in relation to forces from the outside. The starting-point of this view forms the stimulating train of thought of VAN LEEUWEN (21, 22) who takes the line that in each relation — including the ordering relations forming the base of organization and formation of structures or patterns, both inherent to life — elements of communication and isolation can be distinguished. The leveling elements or elements of communication with forces from the outside are represented by the regular supply of organic material (tidal drift) and sea-salts. The spatial differentiating or isolating elements consist of a relative shelter against wind-blown sand and sand thrown up by floodwater and of a limitation in the composition of the tidal drift to prevailing brown algae. Along our beaches the aspect of shelter can only be realized at coasts with a very differentiating structure in the direction of the coast-line, viz. by re-entrant and salient angles. The habitat in the Netherlands shows these characteristics, as well as the habitats of P. maritimum described in literature. From the view-point of nature conservancy it is of the utmost importance that coasts showing the above mentioned structure in the direction of the coast-line are not interfered with.