It looks like a narrow leafed plantain, so would normally be called a weed.

Thank you Bulbaholic I thought as much, but you make it sound so interesting.

There is an 'ornamental' version with double green flowerheads, sold as sterile but I don't believe it.
My mother grows it, and it gets everywhere.

It is a narrow leaved plantain and is a 'native' plant ie a weed if its a nusiance. the roots are relatively easy to get out just dont just pull the top growth off or it will regrow.

I've been trying to remember the botanical name for this all day. I knew the genus Plantago. I've had to look it up and it is P. lanceolata.