The remarkable thing about it are the spiny fruits, I said a shrub but it could also be a young tree.. Location is the rainforest around Paraty.

I got the genus name from saltcedar: Allamanda
Only 3 species occur in the state of Rio de Janeiro
http://floradobrasil.jbrj.gov....
I think Allamanda cathartica is the best match!
http://www.google.be/imgres?q=...

I'm not sure Myriam, the leaves on all look similar or different depending on which photos you find! Allamanda cathartica looks to have broader leaves..

http://www.hear.org/starr/imag...

Allamanda schottii looks closer but it says it's 'bush' but maybe yours was drawn to the light?

http://www.hear.org/starr/imag...

Allamanda oenotheraefolia is possible, if this photo is correct, the species name does suggest leaves like oenothera.

http://www.flickr.com/photos/k...

Thanks Janet! I originally had decided for Allamanda cathartica because of the best resemblance of the fruit; the spikes on mine are very long. I think the leaves look much bigger on mine than the two other species.
In this link the leaves look very similar to mine, they also describe the length can reach up to 20 cm, on other sites up to 14-15cm but that would still fit.
http://fr.wikipedia.org/wiki/A...

The length of the leaves for Allamanda schottii look smaller and it is described as a vine..
I'll try to find back the picture with the fruit..

http://www.google.be/imgres?q=...

On this site the length of the spines is described as 1cm long! (but the ones on mine do look longer than that even..)
http://www.prota4u.org/protav8....

Capsules subglobose, 3-7 X 3-5 cm, with spines to 1 cm.

leaves elliptical to obovate, 2.5—15 cm x 1—5 cm

The fruit also seems to be long spined though with Allamanda schottii but is described here at a maximum height of 2m. Mine was much taller.
http://www.prota4u.org/protav8...

The leaves on Allamanda oenotheraefolia look a bit too small on the picture you found Janet, certainly too small on this picture;
http://search.babylon.com/imag...

On this site it is described at a max. height of 2,5 m, too small and it has arching branches.
http://mobilearn.np.edu.sg/flo...

Allamanda cathartica is described here with a height up to 6m which does fit better.
http://keys.trin.org.au:8080/k.....

Aha, with seeing the flowers of Allamanda, I found another in my unidentified Brazilians that looks like a match for Alamanda oenotheraefolia. This one was taken in Rio de Janeiro town.
http://www.flickr.com/photos/m...

I think many sites are showing the incorrect photo for the species Myriam! The photo of Allamanda oenotheraefolia you linked to was at least taken in a nursery in Brazil so is probably correct.

The plants of Hawaii should also have the correct plant, the flowers of Allamanda cathartica and schottii in these photos don't have a long tube.

http://www.hear.org/starr/imag...

http://www.hear.org/starr/imag...

Heights given on many web sites are often not correct either, they usually reflect what the plant might grow to in 10 years and in a different climate.

Alamanda oenotheraefolia has to be correct, good job you found a flower photo.

I checked the Hawaii site again, one photo of A. cathartica does have a long tube although the photo was from Home Depot. Maybe they have two types of flowers, male and female?

Look on Tropicos ..

http://www.tropicos.org/ImageS...

It's very difficult to say for sure!

Problem is that the plant with the flower (in Rio town) was not the same as the one in the rainforest with the spiky fruit, that last one had no flowers.
The pictures on Tropico look different again than on other sites, very confusing..
But I guess you're right, it might be better to keep both as Allamanda sp.