Which brassicaceae?

A couple years ago I got seed through the exchange for "Petrocallis pyrenaica". One seedling survived, bloomed a bit last year, and is blooming again on a slightly more robust plant now. It's clearly not petrocallis - probably some kind of alyssum, aurinia, or something in that botanical corner. Any ideas? My page about the plant is up here: http://www.robsplants.com/plants/PetroPyre2 and I'd love to get the identification correct.
Thanks in advance for any suggestions!