I saw this blooming at the US Botanic Garden in late February 2012. I labeled the photo "Rhipsalis," mostly because it was after a series of Rhipsalis photos. I don't think this had a visible tag--probably hidden among all the plant growth--so I don't have a photo of its ID. But, on the basis of its segmented shape that looks like bottles attached end to end and the yellow flowers, I'd call it Hatiora salicornioides.
