Apparently it is a native of S America. A plant self seeded in my neighbour's garden last year and he saved some seed. It has a very unusual leaf when it is immature - vibrant green with black speckles. The flowers are a beautiful shade of blue, but very short lived and then they form Chinese Lanterns.
I think it is related to the Nightshade family and rumour has it that it is an insect repellant ...
Think it is still fairly unusual in the UK, although it seems it self seeds as it is one of the varieties included in bird seed.
I've not managed to get a good picture yet, but here is a link to the RHS description:
I'm collecting the lanterns as apparently the seeds are prolific, so if you would like some let me know :)