Unidentified tree

Question

There is an empty lot near my house in Portugal. Sometimes we would throw the seeds of whatever interesting fruit (e.g. cherries, avocados) we were eating into the lot, with the hope, though not expectation, that perhaps some trees would grow there and yield fruit. It is entirely possible that people from other houses adjoining this vacant lot also throw some stuff there.

Well, there is a tree growing now, with fruit. Sadly, it appears to be badly infested. I am not at all familiar with fruit trees, so I am not able to identify the fruit. The fact that the fruit and leaves are in poor shape due to the infestation does not help me when I try to compare my photos to online images.

Can you help, please?

Thanks in advance.

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Answer 1

I think this is actually an oak tree, and that what appear to be fruit are actually galls, or abnoral growths caused by an insect infestation. The tree might be a Holm oak. I'm not sure what species, but the galls are probably caused by a wasp which lays its eggs in the tree. Here is an article about them:
https://entomology.ca.uky.edu/ef408

Answer 2

Very interesting!

Having now looked at various online images of galls, I can see that there is quite a similarity between some of those and "mine".

Thanks very much for solving the mystery.

Cheers.