This little inconspicuous orchid could easily have escaped my attention, it was growing amidst dense vegetation at the side of a trail, nearly choked out. It must have had leaves but only a small fraction of one leaf was left, not worth photographing.The height wasn't bigger than 20 cm or maybe even less..
The conditions weren't ideal for photographing with the bright midday sun hitting it and the busy background of the surrounding vegetation.

Anyone has an idea to what genus it could belong?

What did the leaf look like? Did it look like a rosette? Were the leaves growing up the stem? Shape?

I have no clue really but it reminds me of Eulophia: https://garden.org/plants/sear...

I wasn't sure if Eulophia grew in Brazil but googled and found this page: https://translate.google.com/t...

I am really bad at trying to compare photos but it also reminds me a bit of Oeceoclades:

O. maculata was first described in Brazil in 1829: http://www.iucnredlist.org/det...

It sure looks a lot like your pretty little Orchid: http://www.microsofttranslator...

Oh Lin, I believe you've hit the nail on the head!
It certainly looks like a match with Oeceoclades maculata!
And the 'Flora do Brasil' has Oeceoclades maculatai as the only species of the genus present in the Rio de Janeiro state!
http://floradobrasil.jbrj.gov....
The bit left of the bug shewed leaf of mine gave the right hint of the shape shown on the photo of the species. It seems to only have one leaf at soil level.

Myriam, glad to help and thank you so much for the 's!