NOTES ON RUMEX ACETOSA L. IN THE BRITISH ISLES. (BElT RAG ZUR KENNTNIS VON RUMEX No. XV)*

After having monographed Rumex for all the continents except Europe, and after having published a treatment of the central European species in the second edition of Hegi's Flora von Mittel-Europa (1958) and written one for "Flora Europaea " (unpublished) it became apparent that most of the major taxonomic problems have been solved more or less satisfactorily except two. One is Rumex crispus L., of the subgenus Rumex (formerly Lapathum), a polymorphic species evidently comprising several races characterized by slight morphological differences, some of them also ecologically different. But all these races are evidently interfertile and some of them are extremely invasive, and by their extensive spread and interbreeding they seem to have obscured the original distributional pattern of the other races. The second problem still unsolved is Rumex acetosa L. in a broader sense. In my treatment of Rumex in Hegi's Flora von Mittel-Europa as well as in "Flora Europaea " I had to admit that the treatment of this species and of its allies is still a tentative one and far from satisfactory. The traditional way of distinguishing R. acetosa from the most closely allied European species is as follows