Colocacia was my first thought but could be some kind of Philodendron.

Was it grown as an epiphyte (grown on a host plant or false cork tree etc)

My first though was Philodendron maximum, although the leaves are not really dark enough..........

Hmm, maybe.......I did ask one of the nursery people....they didn't have a clue. I am still searching. I love its lime green colour.