Silene vulgaris, bladder campion, I believe.

Bladder campion?

interesting plant.
i wanted one until i found you need a male and female
not self fertile.
tastes like spinach, but you can eat it in the summer !!

Here is a link that might be useful: http://www.pfaf.org/user/Plant.aspx?LatinName=Silene+vulgaris

Silene vulgaris is not exclusively dioecious. Some plants are monoecious and some are hermaphrodite, i.e. it occurs in the different forms. Hermaphrodite is the commonest form.