OK, I have found more which are possibles! Senna macranthera var. macranthera which has a more recent collection date, the leaves look good for that too and the flowers even though dried look much like yours! Senna neglecta looks possible too!
If the search doesn't show, select country Brazil, 'any' in all fields but the genus where you can select Senna.. there's three pages.
http://ww2.bgbm.org/herbarium/...
Senna occidentalis and Senna racemosa var. racemosa have similar leaves but appear to have more leaves per stem.
More research, see if I can find some more flower photos.