Thanks Stevo for the id. I think you are right, it is a vexator.
Hi, it really looks like vexator BUT! at Paraguay? Ciudad del Este? I was there when I was 15 years old, it is a subtropical place... but the blue jaboticaba grows at Venezuela (tropical climate), 3500 kilometers to the north... so, the paraguayan M. vexator trees should belong to a paraguayan collectionist!