(B. pubescens Ehrh.), the Old World counterpart of B. papyrifera, occasionally escapes from cult. It is more stiffly erect, with evidently resinous buds and mostly smaller lvs (3-5 cm on the fertile shoots) and pistillate catkins (1.5-3 cm). In Eurasia it is largely confined to wet habitats, whereas B. pendula grows in ordinary well drained soil.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.