Posted: 22/07/2014 at 10:49
I think it may be Cyperus Alternifolius (umbrella plant). It has appeared in my garden too - just one clump at firtst, which I didn't knowingly introduce. But this year I've noticed it starting to spread, with seedlings appearing here and there.
I rather like it - it looks impressive in flower arrangements or just by itself, a few stalks in a vase. But I think it has big ambitions and I intend to keep an eye on it.