I was given this plant by a co-worker, who didn't know what it was. I have been told variously that it was a dog tail cactus, a monkey's tail cactus and a rat tail cactus. But its flowers don't look like the flowers on any of those cacti. They look more like oxalis flowers. The buds appear, folded up, on thin stems that shoot straight up. As the flower unfolds, the stems bend and droop. The flowers last for weeks. Also, the spines on this plant are not sharp -- they are soft, more like hairs.
Those are not flowers but the leaves of an oxalis plant. There is an oxalis plant embedded somewhere in your cactus pot. As far as what type of cactus, not sure.
I agree on the leaves being of Oxalis. Somehow, it got mixed in with your cactus. The other looks more like Stapelia except for the spines.
It looks like a rat-tail cactus to me, I got a good laugh about the oxalis "flowers".
You may have trouble getting the oxalis out . . . they are bulbs and will come back if you don't get the bulb out.
It's a nice oxalis so if you manage to remove it replant the bulbs in another pot.
Yes, Oxalis triangularis http://davesgarden.com/guides/pf/go/1241/
Possibly a Disocactus. http://www.desert-tropicals.com/Plants/Cactaceae/Disocactus.html
Thanks! You know, it never occurred to me that there were two plants in that pot. Now I know why the "flowers" looked so familiar. I'm not going to remove the Oxalis, though. I get a lot of comments on my cactus with the funky flowers!
Disocactus speciosus (Looks like it could use a little more light)
(4th photo down) http://www.rud-epis.de/04%20RUD%20Epis/epis/kirsten%20pfeiffer.htm
(Thumbnail #12) http://www.cactusinfo.net/gallery/D/index.htm
Here is the D. speciosus page in the PlantFiles for submitting your photo to the database: