MUSTARD?

Not sure what this is - it's a pretty weed that has incredible tenacity - I believe it to be a member of the mustard family...

Lost my Keble-Martin Concise British Flora - nearest likeness I could find in Culpeper was "White Mustard"?

It's the one which bleeds bright egg-yellow sap when broken which stains the hands dark brown when you molest it. The sap is alleged to be lethal to warts...

Old wives' tale!