It clearly looks a member of the Pea family (fabaceae).
It was growing on a waste or clearance land in a rainforest area in Paraty. It was tall,( around 2 m) airy and very broad too.

Cassia, I think.

The foliage resembles Senna corymbosa but the flowers don't look right to me. http://toptropicals.com/cgi-bi...

Where's our super sleuth Janet? I bet she might recognize this one!

Well, I was just googling for another plant and came across this one, a member of the Pea family, Cajanus cajan:

http://www.tropicalforages.inf...

http://www.google.com/search?q...

I think it's Crotalaria, if it is there's a lot of them!

http://www.google.co.uk/search...

http://en.wikipedia.org/wiki/C...

Ahhh, I wasn't sure, that's why I wrote "I think", Cassia has those rounded leaves, should have paid more attention.

Crotalaria pallida looks possible..it's in the area.

http://www.google.co.uk/search...

http://www.hear.org/starr/imag...

Thanks Sue and Lin for trying to help!

Crotalaria pallida feels right, Janet!
I looked through all the other species in the list and pallida comes out as the best match.

http://floradobrasil.jbrj.gov....

Thanks a lot!!

I just realised you can search for the region too which makes it much easier than clicking on all the species in the list! It certainly makes an easier job of it if you know the genus.