It might not be possible to find out the species, but I put it up anyway..
There are 38 sps. in the region,
Mimosa bimucronata is the closest I found, but the flowers of mine are not so pristine white, more yellowish white, and the flower head in bud looks more elongated..
https://www.google.be/search?q...

No match here either for Mimosa..
http://www.ufrgs.br/fitoecolog...
I googled all 38 sps, phewww.. most of them have no pics on the web..




I think this one could be the same species, it was a tall tree I met in a large community property..

Looks like Leucaena leucocephala, White Lead Tree / Haole Koa (Hawai'i)

http://wildlifeofhawaii.com/fl...

http://plants.ifas.ufl.edu/nod...

http://plants.usda.gov/core/pr...

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

Leucaena leucocephala has naturalized in Brazil! (How much it looks like a Mimosa! )
I think that is correct for the tree!
I took a crop of one of the pics, and its flowerheads look round.


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

But my shrub might be something else, I'm still thinking about the elongated flowerbud heads..
The leaflets look broader too..

Dave!

You're very welcome!

The tree has naturalized throughout Hawai'i. Originally introduced for cattle feed.