Poncirus trifoliata is correct, I think

That's it! Or at least some type of trifoliate hybrid. Where are you located just out of curiosity?

Kristopher

Awesome, thanks. I'm from Auckland, New Zealand. I'll attach another photo which better shows the inside leaves which look a little different. I am wondering now if the trifoliata branches are emerging from the rootstock and it is in fact a different citrus type above it which goes with the seemingly dead trunk.

I really want to grow one but have been unable to find any seeds. Is it possible to propagate by cuttings at all?

Cheers, Henry.

Henry you're right! I didn't even notice those other leaves. Looks like maybe it's a type of orange? I'm not very good at identifying but if you cut the rootstock suckers off you might get a tasty tree! I've heard it's hard to get poncirus to root from cuttings but its worth a try. I would think it would be a good idea to give cuttings bottom heat to aid in rooting and maybe try a rooting hormone.

Kristopher

Thanks for your help Kristopher I'll do some reading and attempt some cuttings tomorrow!

Henry

The dead stump is the original citrus variety, and all the tri-foliate leaves are from the poncirus rootstock. As the top variety has re-sprouted it could be saved. You - or the park gardeners - should cut away all the rootstock growth and remove the dead part above the new growth.
With a bit of weeding and feeding and TLC it could produce fruit in a couple of years or so.