There's so many different Senna specis Myriam, I was trying to find some more photos showing the leaves better but I can find only similar leaves and flowers.
I thought Senna corymbosa might be a candidate, but the leaves maybe don't look right.
I found flowers with the same shape, Senna barronfieldii but it's not in Brazil even if the leaves don't match.
http://www.rainforestpublishin...
Senna septemptrionalis is in Brazil, the leaves are glossy but I'm not sure about the flowers.
http://www.rainforestpublishin...
The flower habit is more like Senna corymbosa, I'm really not sure!
