Jeff, I know they are in the same family, but it is confusing because there is Tulip wood that is exotic. Cottonwood and tulip are poplar (poplar family) and greenish to white/off white, yellowish color and have sometimes a dark(er) heart wood. Believe me, I have read all weekend on it and it is still confusing! But yes Tulip Poplar and what is called cottonwood is where the mineral stained come from from what I gather.
Mike
Well I keep adding to this...One site says the Tulip Poplar is not a Poplar at all?

/(go figure). I talked to one sawmill that actually say they trrow away the dark (mineral stained poplar because of no meaningful market but "crafts" (he now has a new appreciation and phone number) The mill I know keeps some says they seldom have anyone ask for it. So muck so that they put it in a shed at the back of the mill. Well I keep researching. I love doing this. I get to find out how dumb I really am!!!