It seems a species of Cyperus.

Genus : Cyperus

check Cyperus compressus

It looks like Cyperus, I think Ram is right can be C. compressus

I think Cyperus compressus L. is a good suggestion.

Eduardo et al.:

Yes, shows close affinity with Cyperus compressus but the documented specimen is quite different.

Best

Syed

I think cyperus compressus but your specimen is different

 Cyperus compressus parece ter talos Mais longos que esse especime

Eduardo:

What do you wish to show? The details in the Herbarium material of C. compressus cannot be seen. 

Best

Syed

the short culms. also found similar with Cyperus breviculmis F. Muell.

Eduardo:

Yes, C. breviculmis looks extremely close.

Best

Syed

It seems Cyperus breviculmis...

Does Cyperus breviculmis is synonymous of Pycreus pumilus?

data base The Plant List and Tropicos

http://www.theplantlist.org/tpl1.1/record/kew-260443

Yes Cyperus breviculmis F. Muell is synonym of Pycreus pumilus (L.) Nees.

Surely this sedge is Pycreus pumilus

http://www.hkwildlife.net/Forum/viewthread.php?tid=61295

Eduardo:

C. breviculmis is a synonym of P. pumilus. and closely matches with your documented specimen.

Best

Syed

It seems Cyperus squarrosus L., native in Brazil, because of the slightly excruved awns.

Best wishes

I suggested this species, synonymous with Cyperus squarrosus L.