I don't know why I didn't take better pictures of the plant at the time I found it growing wild on the beach of a small island in Mirim-Paraty, but there was so much to see and time was limited! The Cactus was full of closed flower buds but ready to bloom, it downed to me it might be a night blooming one, so took one of the ripe buds 'home'.
Sure enough that night it opened up!

So far my searches have lead me to think it being a Cereus species, it will be unlikely to get a species name but I would like to know if I'm right with the Genus..

I think so, yes.

Thanks Hetty!

There's not many Cereus in the list Myriam, I found by clicking on the name it brings up a map usually giving locations. There was two species more likely than others althougha couple came close to the location. Look at Cereus fernambucensis..

http://www.flickr.com/photos/3...

Flower sure looks very similar!

I have looked up some more details and it should have between 4 and 6 ribs. And this particular Cereus (known locally as Mandacaru) is a Brazilian native.
I think she's got it!! Excellent sleuthing.

Myriam: That is one beautiful Cereus! Looks like Super Sleuth Janet got the ID correct ... at least it certainly looks like that's the one!

If you can get past the BRIGHT pink background of this page, here's a bloom photo I found while googling: http://www.fotolog.com/mariaco...

and another bloom photo here: http://www.flickr.com/photos/3...

That is it!!! Once more an amazing find Janet! It was some time I had been trying to find its ID, and I did see the short list of natives, but only found pictures with the genus name when googling them!

Thanks to all for the kind help!
I see the photo on flickr shows the cactus blooming at daytime, so not a night-blooming one then, maybe if I had been on that island one day later I would have seen it blooming in its full glory and probably would have taken tons of pictures!

Wikipedia (and several other sources) say it is night-blooming.

I thought so too Hetty, I wonder how the person on Flickr got a picture in daylight..

There is a shadow in the pic on flickr, I did wonder if they had set up a light source to take the photo, a flash wouldn't show a shadow. A light source from behind might have, unless the flowers opened just as the sun was setting. It is one of the two given for that area, I checked another which was close to the area but it didn't fit.

Cereus jamacaru distribution is close to the area, but it doesn't match as well, click on the name to see the area they are in.

http://www.brazilplants.com/ca...

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

I looked at the photo you linked to with the bright pink background Lin, it has bright light with shadows too indicating it flowers in daylight.

Thanks Janet, very curious! Still Cereus fernambucensis remains the perfect match, I don't feel the same with Cereus jamacaru .

'Night blooming' cactus flowers in my experience are usually still open until around 9 am.

Aah, that explains it Hetty, thanks!

I have two night blooming Epiphyllum cactus. The Epiphyllum oxypetalum blooms are always finished by morning but the blooms on E. hookeri are sometimes still open at @ 8:00 a.m., and once there was a bloom still open at one o'clock in the afternoon.

My Epi. oxypetalum stayed open during the day it's first two years from a cutting. After that it has only bloomed at night.

Nice to know about your experiences with 'night-blooming' Cactus Lin and Carol!