Morphological variation was analyzed in the endangeredBetula uber and sympatric dark-barked tree birches,B. lenta andB. alleghaniensis, to determine the extent of differences among the three taxa. Univariate and multivariate analyses of leaf and fruit characters indicated that the three taxa are morphologically distinct, thatB. uber is more similar toB. lenta than toB. alleghaniensis, that intermediates betweenB. uber andB. lenta do not occur, and that leaves are necessary for absolute separation ofB. uber fromB. lenta because of overlap of fruit characters. Field observations of the bark indicate no differences betweenB. uber andB. lenta while those of growth form suggest thatB. uber may have a more compact crown thanB. lenta. The evidence presented here supports an alliance ofB. uber with the dark-barked tree birches (seriesCostatae).
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