644 Polygonum raii Bab.

The species (or subspecies) and lower taxa in this critical complex are mapped separately, viz. P. raii Bab. s. str. (subsp. raii), subsp. norvegicum Sam., P. oxyspermum Mey. & Bge. and P. polyneuron Franch. & Sav. Some of the occurrences may be casual or extinct. (Cf. the nomenclature used in Fl. Eur. 1/1964, p. 78, and the mapping in Atlas Fl. Eur. 4/1979, map 397.) The occurrences in eastern N. America are introduced. Apart from the Japanese P. polyneuron, very closely related to P. raii, this complex has an amphi-atlantic distribution (Hultén, Amphi-atl., p. 288 and maps 269 och 270).