This is a hypocotyl graft of a Selenicereus megalanthus seedling.
It appears to have achieved union with the Pereskiopsis rootstock but growth is not happening. Not unusual, I have some seedling grafts to Hylocereus which are >1yr old, they are still alive but that's all.
I will remove the scion and try it on a Schlumbergera rootstock, not hopeful of success, nothing to lose though.
