I found them in a small group growing in the shade of a rock close by the river. They seemed to be in the early stage of blooming with yellowish flower buds emerging. Unfortunately I didn't get the opportunity to go back later to see them in full bloom.
Anyone has an idea?

Makes me think Iris

Thanks Daisy, but there are no Iris species native in Brasil.

My first thought was ginger of some kind.

According to several studies, there are 160 Iridaceae species in Brazil.

Maybe a Neomarica.

Oh yes Daisy, you're right, i didn't think of family members of the Iris.
The Rio de Janeiro state, where I found the plants, has 8 genera and 25 species.
Neomarica is amongst them.
http://floradobrasil.jbrj.gov....
I'll have a look at it tomorrow with a fresh mind..need some sleep now..
Thanks!

It definitely looks like being in the Iris family..

Sisyrinchium vaginatum is a possible candidate..
https://sites.google.com/site/...
http://www.brazilplants.com/ir...

My plants were not taller than about 20-25 cm..

The leaf fan shape and the flower hardly having a visible stem looks very much like Neomarica altivallis like in this photo:
http://www.brazilplants.com/ir...
Problem is it states a height of 70cm and isn't supposed to occur in the Rio state.

Neomarica longifolia might be a better candidate..
http://www.brazilplants.com/ir...

But as we have no open flowers it might be impossible to find a definite identity..so better leave it at that.

Hi Myriam

The form does look like Neomarica, except I'm not sure if the plant leaves arise from a stem like yours does. I had a couple of Neomarica I grew from seed, they grew quite well in a greenhouse until a cold winter killed them off, from what I recall the leaves fanned out from ground level. Does anyone know of a Neomarica which has such a stem?

https://www.google.co.uk/searc...:

That might leave us looking in a different family. The only other family I could think it would fit in is Orchidaceae.

Thanks Janet for popping in!

JRsbugs said:
The form does look like Neomarica, except I'm not sure if the plant leaves arise from a stem like yours does.

yes, that is also a question I had!
Also the fans of mine are very flat as if having been pressed and we have the problem of the size that doesn't seem to fit Neomarica sps as far as I found out. The plants were also growing in deep shade..
Good you're suggesting to look into another family; the Orchidaceae..

There's 140 Orchidaceae generea with 831 species in Rio de Janeiro!

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

I'm now realizing this..deep sigh..