At first they seemed to be palms but then when I found pictures of Palm Grass (Curculigo capitulata) I thought I had found its id. But not as the plant doesn't occur in Brazil in the wild according to the Flora do Brasil.
I also considered it could be young palms, but I haven't met a bigger one it could be. The max size. I've met them was around 1.20m (4ft) usually in deep shade.

Maybe Asplundia sp. ? https://en.wikipedia.org/wiki/...

edited to add a couple more links:
http://www.researchgate.net/pu...
http://www.freebase.com/m/02q4...

Thanks Lin, yes Asplundia has a great similarity to my plants, the only problem is that the leaf blade of Asplundia seems to be always split in two halves, which mine doesn't have..

I'm always forgetting to enlarge the pictures! Yes, you are correct, it doesn't appear to be Asplundia. I wonder if it could be the Calanthe genus? https://en.wikipedia.org/wiki/...

http://garden.org/plants/searc...

Curculigo capitulata has escaped into the wild Myriam, read Monocromatico's review ..

https://www.google.cz/search?q...
https://www.google.cz/search?q...
https://www.google.cz/search?q...

Palm Grass (Curculigo capitulata)

Thanks Janet for that valuable info! And the commenting person was from Rio so that makes it all more credible!

We are so very fortunate to have our Super Sleuth Janet as a member here at ATP!