Irish walnut hardwood comes from two species, the European walnut (Juglans regia), and American or black walnut (Juglans nigra). Both are only occasionally found growing in Ireland but produce excellent and highly prized timber.
European walnut can be quite variable in colour, ranging from a lighter pale brown to a dark chocolate brown with darker brown streaks. The colour can sometimes have a gray, purple, or reddish cast and can occasionally also be found with figured grain patterns such as curly, crotch, and burl.
American black walnut is generally darker and more uniform in colour.
Source: National Council for Forest Research and Development