I believe the latest scientific opinion (which does keep changing) is that the black morels we have here in the eastern US are all mostly the same mushroom, Morchella augusticeps. See the discussion on Mushroom Expert's site:
http://www.mushroomexpert.com/morchella_angusticeps.html
The ones that are really confusing are the so-called "tulip" or "deliciosa" morels, which do have multiple forms