Thank you @elivings1. I did see that article already. I didn’t find any actual description of leaves and bark, and no pictures.
I would like to figure out what rootstock I have now, rather than years down the road, for 2 reasons.
The first being that I have dug up some of the suckers and transplanted them. I will graft some cherries to them if they are Mazzard. If they are Mahaleb, I may as well not bother as they will not thrive in our soils. I don’t want to waste time, effort and scions on those rootstocks. I have my cherry trees planted in raised mounds to aid in drainage, but I expected more growth than I currently have, so I am wondering if they are on Mahaleb rather than Mazzard.
So the second reason for wanting to determine the rootstocks now, is to keep good records of what rootstocks work for me here, and which ones don’t. If they are Mahaleb, I will want to think about planting their replacements sooner rather than later.