Dioscorea polystachya vs. Dioscorea japonica?

I apparently successfully overwintered a yam that I grew from one purchased at a local Asian market (which was a surprise to me, since I thought it was dead... and so did the contractor we had out on the property that tossed the seemingly empty pot aide.)

I'm not sure which species I ended up with, though I'm almost certain that it's either D. polystachya, or D. japonica. Can anyone who's grown both post some comparison photos so that I can nail down which I've ended up with?

Also, do both species produce edible aerial tubers? That's my primary interest in growing yams, though I'm not opposed to digging up the main yam if I need to.