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.
