Taxonomy of infraspecific variation in<i>Betula pubescens</i>Ehrh., with particular reference to the Scottish Highlands

Abstract

Synopsis The 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 of Flora Europaea , sspp. pubescens, carpatica and tortuosa . Two subspecies are recognized in Britain, namely ssp. pubescens and ssp. odorata , but some confusion has arisen through the undetermined relationships between sspp. odorata, carpatica and tortuosa . The rejection of ssp. odorata is 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. tortuosa and ssp. carpatica are probably indistinguishable (a conclusion supported by multivariate analysis) and that the epithet tortuosa can be applied to both taxa. The pubescent birch in the Scottish Highlands may be referred to ssp. tortuosa and, 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. microphylla Hartman.