Looks quite like Papyrus. Can't find an image 4U.
Have a wee Google©

Papyrus. Likes its roots kept very wet. Not hardy outside in the winter.

agree but will need winter protection too. At work one goes into the pond margins in the late spring and gets removed round about the 15th sept into a cool greehouse.

Dwarf Papyrus (Cyperus isocladus). I would follow Seaburngirl's advice on that, whether what she has is this one, or the big one (Cyperus papyrus).

ours is the 5ft one so the big one :o)

There is one that is hardy Cyperus glaber but is shorter growing. It's evergreen too.

Yep, that's the big 'un, Sbg! Though around here, they get 10 feet tall--I swear! Not a Texas tall tale from Arizona! ; )