Are orchids C3, C4, or CAM plants?

[OliverSparrow]

I've posted here before, but nothing happened. Better luck this time, I hope.

I'm not going to dig for papers, so this is from memory. About a third of orchids have CAM capacity, almost all of the epiphytes. the trait evolved at least ten times, perhaps twenty. That's because all the "plumbing" is there for CAM in a standard C3 plants, and all that needs to change is some reshuffling. To the best of my knowledge, no orchids are C4. All but a few desert chenopods have krantz anatomy - cell sheaths around their leaf vascularisation - and so far as I know there are no orchids which show this.