By road in wet gravel. The leaf had a bitter taste that hit after about 20 secs of chewing, but lingered for several minutes. These leaves don't have the lobes seen on my three other observations posted as being in Genus Barbarea, none of which is validated by anyone.
e.g. https://www.inaturalist.org/observations/111549159.
Perhaps the other three are wrong, but more likely this ID is.
Flowers have 5 stamens, so not C. fontanum or C. glomeratum which both have 10 stamens.
Possibly C. pumilum or C. semidecandrum?