Help identifying rootstock?

[TrashStar]

Hello, everyone.
So, I have this mandarinquat tree that is very prolific as you can see the full tree image, (left is mandarinquat and right top is rootstock I think) also, forgive the no trimming part, I’ve been on chemo so I couldn’t trim it this year, anyway.

I think the rootstock fruit is growing alongside the graft. Problem is, I can’t identify it. I thought it could be a bitter orange, or a volkamer* lemon hybrid of some kind. I thought it best to ask the Citrus experts since it is most definitely two types of fruit in one tree, and the leaves are different on both sides as seen in the images.

The bottom outside core of the big orange is different than the mandarinquat so I know which is which but these are definitely sour tasting.
Thanks so much for helping identify it if you can.

Edited autocorrect villager to volkamer.

[poncirsguy]

I don't know but if you can use both then keep both and trim the orange some to keep it from killing the mandarinquat

[Galatians522]

That rootstock is one of three things. Rangpur lime, Rough Lemon, or Volkamer Lemon. My guess is that it is a Rangpur Lime since you are in California amd it is the most hardy of the three. All three are natural hybrids between acid mandarins and citrons.

[TrashStar]

I don't know but if you can use both then keep both and trim the orange some to keep it from killing the mandarinquat

Thank you. I will do that!

[TrashStar]

I don't know but if you can use both then keep both and trim the orange some to keep it from killing the mandarinquat

Thank you. I will do that!

The big one looks a lot like the Volkamer.
The physical traits like, the button at the bottom of the core are exerted and puffy. When you look closely into it you see an X at the center. It is an acidic lemon, not as tasty as others, like the Meyer which tends to be more on the sweet side, whereas this one, is slightly more acidic towards the end.

I appreciate your insight very much.

I’m going to go with Volkamer. I’m in 9B NorCal and I got the tree at HD hardware store. I know it doesn't help narrow down varieties by vendors but I forgot to mention it in the comments.

[sc4001992]

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