Umbrella Palm plant (papyrus palm), Cyperus alternifolius
The plant is called the umbrella plant because it has a grass-like habit with sprays of foliage at the top of the stems. These sprays of foliage radiate out like the spokes in an umbrella. The stems are rigid and triangular and have a white pith inside.
The pith is the source of papyrus paper. Papyrus has no frost tolerance and should be moved indoors for the winter