This taxon is a natural hybrid of B. occidentalis and B. papyrifera. Its morphology is intermediate between the parent taxa. The branchlets are greenish brown and very resinous, and the ovate leaves are glabrous with blunt serrations. The pistillate catkins are very thick and slightly pubescent. Britton 1904, Furlow 1997. Distribution CANADA: Alberta, British Columbia, Yukon Territory; USA: Utah. Habitat Montane streambanks and lakeshores. USDA Hardiness Zone 1–2. Conservation status Not evaluated.
This is another variable hybrid with no advantages over its parents. It is grown in major collections, including a large specimen at Edinburgh and propagations from this at Wakehurst Place. It has also been introduced as seeds from Montana by Kenneth Ashburner, although the identity of these trees is somewhat in doubt, as in the wild they were very large, which seems improbable for a hybrid involving B. occidentalis (H. McAllister, pers. comm. 2007). Trees in cultivation at Stone Lane Gardens have striking black bark.