It is an epiphytic cactus, probably aporocactus. Epiphytic cacti live up in the crotches of trees in the jungles of mexico and south america. They live in the organic matter found in the trees, like humidity and warmth (cant stand cold) and can take quite a bit of water. You should see it when it blooms. Beautiful flowers, and quite a bit of them.

Oh, wow - I just Googled it. The flowers are terrific!

I had searched for it on Google over the weekend but my "tree climbing cactus" type search terms didn't help me find this particular type.

Thank you!!

Just a shot in the dark (Micro knows more than I do), but when I look at the pictures, it reminds me a lot of Rhipsalis; but as Micro said, it's an epiphytic cactus nonetheless.

Planto

It could well be Rhipsalis. I am certainly no expert in epiphytics. I have about 6 epiphytics, and they are the most common in cultivation. A flower would id for sure, but i dont even know when epiphytics mainly bloom. I guessing somewhere in april.

Selenicereus is my guess - it's not a true epiphyte, as it roots in the ground, but as we all see it's got epiphytic qualities.

I grow Selenicereus pteranthus but and that one in the picture reminds me of Selenicereus grandiflorus. They are almost the same thing.