After looking online at walnut for some projects tonight, I think I have a handle on the terminology. The true walnuts are all members of the Juglans family. The big three are European/English/Carpathian walnut; Black Walnut, which comes from eastern North America and Claro walnut, which comes from western North America. What you get if you get walnut without modifiers is almost certainly Black or Claro walnut. The European stuff is apparently very expensive and rather hard to get.
There is also Butternut, which is sometimes called 'white walnut'. It comes from North American and is light brown but has working properties almost identical to the various black walnuts, at least when it comes to carving.
Next on the list are the tropical walnuts, many of which are members of the Juglans family. They include Peruvain walnut and, I believe, African Walnut. They look pretty much like the North American walnuts, but I don't know anything about their working properties.
Finally, just to confuse things, there is New Guinea walnut and some other so-called walnuts which aren't walnut at all. They're not members of the Juglans family and at least in the case of New Guinea walnut, don't look anything like any walnut I've ever seen.
--RC
Sleep? Isn't that a totally inadequate substitute for caffine?