Pot #2: this one was free. It is sprouting from the bottom, but I can't see a clear graft line. It's possible it was above the chopped part. The new growth has long narrow leaves.

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Pot #3: this one was also free. It looks like it is just the rootstock. I'm interested in that too, as I'd love to try some grafting.

Any ideas about what these are? Thanks!

guessing as follows:

1) grapefruit pummelo

2) orange

3) volk rootstock

Here are the two now-separated trees from pot #1. The one one the left does have a grapefruit/pummelo petiole. But it also has a remnant of a cut main trunk, so it could also be a rootstock. Though I don't know of a rootstock that has those petioles?

The one on the right, which is definitely the rootstock only, looks like this, with small leaves and short, numerous thorns:

Guesses? What I can't figure out is, if the tree on the right was grafted, why the heck was it in a pot with another tree? I love a good mystery but also would love to eventually solve it...

I crushed the leaves and smelled them. In pot #1, they both have a mild citrusy smell that's not distinctive. #2 definitely smells like orange. #3 definitely smells like lemon. molewacker, looks like you made great guesses!