unknown plant, Buckinghamshire

unknown plant, Buckinghamshire

Observation - unknown plant, Buckinghamshire. Description: This plant does look vaguely familiar to me, but I've drawn a blank in trying to find a name for it, any help appreciated. It was growing on the edge of an arable field on the chalk of the Chilterns.

This plant does look vaguely familiar to me, but I've drawn a blank in trying to find a name for it, any help appreciated. It was growing on the edge of an arable field on the chalk of the Chilterns.