Greenheart could be lignum vitae,and the wood in your picture does look like lignum vitae. I've seldom if ever heard ipe called greenheart, its called all sorts of things like Bolivian/Brazilian walnut, pau ferro, ironwood, tabebuia, etc.
Lignum Vitae is one of the hardest woods, period. Its also expensive and hard to get. I've not worked it, but have several items made out of it, knife handles and flutes. I heard somewhere that it can be toxic. The greenish hue and its super hardness are its virtues, but the grain is kinda plain.