Could anyone identify this from my description? I bought it at a fete
and have loved it all summer:

The leaves look rather like rocket. The flower is a five-pointed star;
the strange thing is that while the flower is mauve/purple from the
front, it is pure white from the back. It has a lovely scent.

Flowered enthusiastically in a small tub all summer, and still has a few
blooms.

Thanks!

--
Klara, Gatwick basin