Cyperus Alternifolius - the "umbrella Plant"
Excellent as a fair-weather pond marginal, or great as a conservatory plant (for the Patio in the summer months) Prolific, fast-growing and quite imposing. Make sure it's always got plenty of water.
I grow mine in large pots without the drainage holes drilled out....
I have cuttings.
Anyone in the UK, want one?