Japanese walnut has been widely introduced to North America through nursery sales since the earlier half of 20th century, being also used for producing horticultural hybrids with the American butternut J. cinerea in order to elevate butternut's canker resistance. The first generation of these hybrids (F1) has been labeled J. ×bixbyi. The hybrids have had enough time to escape and produce backcrosses with either of the parent species, so that instead of the native J. cinerea, whose populations have been decimated by the butternut canker, there now exists a swarm of backcrosses with various percentage of genetic material from either species. Photo 2 of 10