E-Flora BC: Electronic Atlas of the Flora of British Columbia

The geographical range of western bunchberry is almost completely separate from its two parent species, being south of that of northern bunchberry and west and south of that of Canada bunchberry. However, the ranges of northern bunchberry and Canada bunchberry overlap north of the Alaska panhandle, and hybrids between these two species have been found there. These hybrids look like western bunchberry, but they are diploid (no chromosome doubling having occurred) and mostly sterile; only about half their pollen is viable, and they rarely set seed. Current hybridization between the two parent species takes place outside the present range of western bunchberry and apparently has not yet led to the production of allotetraploids there. The hybridization and allopolyploidy that produced western bunchberry took place sometime before the last glaciation, and the tetraploids survived farther south than the parent species and subsequently recolonized an area where the parents had not occurred or had been eliminated.

Source: Extracted from Wildflower Genetics, A Field Guide for British Columbia and the Pacific Northwest (1983), with permission.