Mystery solved!!!
Thanks to Wendy Cutler (UBC Botanical Garden F.) who asked Alex Popovkin on flickr,
who has a magnificent photo collection of the flora in Bahia, more Northern than the Rio state,
https://www.flickr.com/photos/...
who on his turn asked his colleagues from Rio, and got the response that it is the juvenile form of Mikania hemisphaerica.
http://plantillustrations.org/...
The same botanical drawing in the Flora do Brasil:
http://floradobrasil.jbrj.gov....
