Taxonomy of infraspecific variation inBetula pubescensEhrh., with particular reference to the Scottish Highlands

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SynopsisThe variability of the pubescent birch and the probable existence of hybrids between it and two other birches make it a difficult species to classify at an infraspecific level. To some extent, the variation is geographical and to cover its distribution, three subspecies are proposed by the authors ofFlora Europaea, sspp.pubescens, carpatica and tortuosa. Two subspecies are recognized in Britain, namely ssp.pubescensand ssp.odorata, but some confusion has arisen through the undetermined relationships between sspp.odorata, carpaticaandtortuosa. The rejection of ssp.odoratais proposed as its application, in this case, differs from that intended by J. M. Bechstein, the original authority. An examination of the literature indicates that ssp.tortuosaand ssp.carpaticaare probably indistinguishable (a conclusion supported by multivariate analysis) and that the epithettortuosacan be applied to both taxa. The pubescent birch in the Scottish Highlands may be referred to ssp.tortuosaand, in addition, the high frequency of small-leafed individuals in some populations in the northwest and at higher altitudes, justifies the further distinction of var.microphyllaHartman.