Hi all, this is my first post on this site. Can anyone identify this plant that is growing in my mum's garden. She didn't plant it, has no idea where it came from. She is a keen garden and has quite good knowledge of plants, however, this one has us all stumped. It is growing in a raised bed, which has for several years now been covered with a large plastic sheet and pebbles. This plant has pushed its way through. The leaves are lily-like and about 10cm long and 6 cm wide. It now stands about 80cm tall.We have done quite a bit of research trying to identify it, but have had no joy. Help someone please!!