Crinum Thaianum
Onion Plant
This large plant will produce leaves up to 60 inches long, so although established plants can be cut back occasionally without harm use it carefully. The ribbon like leaves are 0.8 inches wide. Once they reach the surface they will float horizontally on the water. The onion plant adapts well to the aquarium environment and is an undemanding species.
Origin: Thailand
Max Height: 60 inches
Growth Rate: Medium
Area: Background
Light: Moderate, Bright
Temperature: 72-86 F
Propagation: From Daughter Bulbs
Difficulty: Easy
That's from the "Miniencyclopedia of Aquarium Plants" By Peter Hiscock (yay for citation)
It doesn't mention how to get it to reproduce which would have been helpful..