This name is used for woods from at least a dozen different genera, so it's pretty much meaningless.
What I BELIEVE I show below is a South American wood that is used almost exclusively for flooring and heavy construction (dock pilings, etc.).
In the USA, if you see the name greenheart, there is a good chance that it refers to ipe, but that's certainly not necessarily the case.
web pics:
planks
both sides of a plank and a closeup. These are from the BogusColorVendor so the colors are unlikely
planks listed as greenheart / Cholorocardium rodiei
plank listed as greenheart / Tecoma chrysantha
flooring --- you would think that the flooring people would have figured out that apparently using nails in this wood causes stains to spread in the wood.