I started to go through the list which is very long! I may have found it, in fact I feel almost certain I have! The flower petals are the same shape and colour, the fleshy things at the sides of the longer 'pistil' on yours look to have shrunk but they are there, I think they are the "abaxial stamens". It's the petal shape which matches so well as well as the colour, I have found a lot of species but none have quite had this petal shape.
Unfortunately the photographer didn't post any more photos! You can see a leaf which looks dark green and glossy, could easily be the correct shape as we are viewing it from the tip end. Most I have looked at have been a greyish blue and mostly smaller other than those we have looked at with similar leaves.
Senna angulata var. miscadena (not miscadenia as put) Note the photo was taken in Rio de Janeiro!
http://www.flickr.com/photos/m...
Distribution puts Senna angulata right at the southernmost area where you were!
http://eol.org/pages/641285/ov...
Here's where herbarium specimens are handy! Look at the first photo of Senna angulata, the leaf shape matches well if you imagine yours squashed flat (it has obviously been previously misnamed). Look at the bottom left leaf, even the leaf veins match yours!
http://apps.kew.org/herbcat/ge...
It has to be either Senna angulata or Senna angulata var. miscadena, if you agree with this I would call it Senna angulata and put a note saying it's possibly var. miscadena but there is also var. angulata.
Or, if you feel very brave, I would go for Senna angulata var. miscadena as the location is spot on and the flowers match, the photographer must have known the species or they would not have put the variety name.
I took out the 'var.' in the search, look what I found!
http://sweetgum.nybg.org/vh/sp...
http://sweetgum.nybg.org/vh/sp...
Those leaves are correct!
I got the link from this site with more links..
http://www.theplantlist.org/tp...
There's a drawing of the leaves on a pdf, fig. 7.. notice there's two leaves at the end of the leaf stem and two before, just like yours!
http://www.fzb.rs.gov.br/publi...
