The separation of Betulapopulifolia and Betulapendula and their status in Ontario

The North American Betulapopulifolia differs from the European Betulapendula in having a larger number of peltate resin glands on greyish twigs, leaves with long–caudate tips, and a dense pubescence on the adaxial surface of the pistillate scales. Furthermore, B. populifolia is a plant of acid, peaty, or sandy substrates, whereas B. pendula grows in acid to neutral or occasionally slightly alkaline substrates. The bark of B. pendula exfoliates in long thin strands, whereas in B. populifolia it exfoliates as small, very thin rectangular flakes or appears not to exfoliate at all. The basal parts of older trunks of B. pendula often develop vertical fissures, which never develop in B. populifolia. Analysis of variance suggests that the most useful quantitative characters for distinguishing the two species are scale width and the length/width ratio of the terminal one-quarter of the leaf. Several other quantitative characters are useful discriminators but are not entirely reliable by themselves. Discriminant a...