Was supposed to be something else...

[Peppa]

Got this from a seed exchange years ago. Was supposed to be a rock garden plant I wasn't familiar with at the time (have even forgotten which one, I'm afraid). Had potted up several starts to donate to a plant sale, and checked the tag online. Was completely different. I'm assuming it's a weed; just not sure which one. Any info would be appreciated!

[Tristan_He]

Hi Peppa, looks like a wallflower (Erysimum) of some kind. I grow E. helveticum which is similar to this, though the flowers are a bit bigger in my form. I don't know this genus too well though.

I wouldn't say it's a weed, but it would not be the first time something unexpected came through a seed exchange...

[Claire Cockcroft]

If it has inflated seed pods, it might be Alyssoides utriculata.  It is blooming in my garden now.

It can be a ferocious seeder, so I deadhead it while leaving only a few to replace older plants.
...Claire

[Rick R.]

Alyssoides utriculata often gets into the seed exes masquerading as Erysium.  These are Alyssoides seed pods:

[Peppa]

Thanks to everyone for your replies! It's the first time that it's flowered, but so far it certainly resembles Alyssoides utriculata. I'll keep an eye on it to make sure. (Incidentally, I found the original tag of what it was supposed to be - Physaria kingii. The yellow flowers were the only thing I could find in common...)

(And thank you Maggie for rotating my picture 90 degrees. For some reason I couldn't make it stand up straight!)

[Claire Cockcroft]

Here is one of the plants in the scree, with some seedlings in the background.

[Peppa]

Thanks Claire for the picture!