Unknown Brassicaceae at NARGS forum

[Lori S.]

Hi,
An identification request has come up at the NARGS forum for a misidentified Brassicaceae of some sort:   
https://www.nargs.org/forum/not-arabis-androsacea#comment-26944

I'm at a loss as to what it might be but it's very likely that someone here will know what it is!  Thanks in advance!

[Maggi Young]

Isn't that an Iberis of some sort?

[Lvandelft]

I've seen this plant more often seen at plantmarkets, sometimes even as A. alpina... , I believe your plant is biennial?
But it is most likely Arabis pumila or Arabis turrita.

[Lori S.]

A photo of it in seed has now been added to the NARGS thread.  From the long, narrow seed pods, it looks like Iberis would be out but that it could well be an Arabis?

[ChrisB]

I have the same plant. John Richards told me its Arabis aubrietioides

[ChrisB]

Oh, and in my garden it is perennial, had it about 5 years now. Seed devilishly difficult to extract!

[Maggi Young]

I'm surprised the leaves are not more dentate. ....... 

[plantrob]

Hi,
I'm the original poster over at the NARGS forum. Thanks for chiming in with your suggestions. I've looked into the ones suggested thus far, and none of them looks quite right. Maggi is correct that the leaves on my plant don't show enough dentation to be A. aubrietiodes. Similarly, the leaves on A. turrita are quite different: less succulent (floppier), and stem leaves are much larger (extending well beyond the perimeter of the flowerhead). A. pumila comes closest, and might be right if variability in the species is taken into account: the leaves are about right, but the flowerheads in pictures online show clusters of fewer, larger individual flowers than I've ever seen on mine. Also, the stems on A. pumila appear to be wiry and darker, as opposed to fleshy and mid-green as on my plants.
Still hoping for more suggestions