I got a bit closer by my half-Brazilian friend who says the popular name is 'Mata-Cavalo' which means 'Horse Killer' !
many different species seem to be named Mata-Cavolo though..
But for sure it in the family Solanaceae..
There is an enormous list of Solanum species recorded for the State of Rio de Janeiro!
http://floradobrasil.jbrj.gov....
I have done a big bunch of that but haven't found an exact match yet. I think I'll have to leave it as Solanum sp.
