I'll see if I can take new photos, today. The leaves are very thin and the stems are elongated.

What do the basal leaves look like?

I believe this is the plant. The flower were closed this morning...

Sorry that’s not really helping. The leaves are wilted so neither shape nor texture are clear. In fact that looks more like the Lapsana than the second plant.

@floral_uk z.8/9 SW UK, my apologies. I'll see if I can take another photo, or see it flowering again.

I hope this photo helps, There are so many weeds growing in this patch that it is hard to find the stem.

Well, I’m stumped. I can’t square those jagged leaves and pubescent stem with the Brassica flowers on smooth stems. Are you 100% certain they go together?

The one with the 4 petaled flowers reminds me a bit of my 'wild' arugula - Selvatica rucola?

Yes. It does look a bit like Diplotaxis tenuifolia, wild rocket, but the leaves we were shown are wrong for that plant.

Hope these photos help

Basal leaves don't seem to match images when I search 'Diplotaxis tenuifolia', but perhaps related?

Well, definitely related because it’s a Brassica. That much is not in doubt.

Floral, what about Hirschfeldia incana? It's not supposed to be in Montreal, but it may be on the move.

The incana bit would suit the pubescent stems.

Thanks everyone for the help.

One thing of note.

This is mostly a poppy patch growing in a gravely parking lot, under a tree. The poppies on my side are stunted and miserable. However, the ones on the patch in front of our parking are twice taller and bigger. (Same seeds).

I assume it must be the same for the Diplotaxis tenuifolia. ...

Growing conditions wouldn’t account for the different leaf shape and texture. I grow Diplotaxis and it also grows wild here. That isn’t what you have.