Dear Gordo Kury, I am not especially familiar with the plants of Argentina. My forays to South America have taken me to Peru and Ecuador on a few occasions. That said, here is some reading that might be of use and get you started.
How about the Phyllanthus genus, either niruri or urinaria, also known as chanca piedra.
A humble little weed found in most of the tropical areas of the world. If you go to Google Scholar, you can find a lot of research being done on its anti-viral, anti-cancer, and other anti-illness properties.
It's coming up all over my garden now. I used to think it a bothersome weed until I researched it more. Now I dry it and use it to make herbal tea.
thank you John!
the biota of the Paraná river delta is very specific, that's why I asked, it's difficult to find anything on google that takes the specific flora of this area in consideration and gives serious information about it. I hoped Arthur might have first hand knowlledge about it, but I'll look those links up later, I'm sure they will bring something handy to the table