Firstly a mistake, the woad on the Humber bank is more likely to be yellow rocket, Barberea vulgaris, associated historically with a young Greek woman, Barbara, killed by Roman soldiers in A.D. 235 and later canonised by the Roman Catholic Church. Vulgaris = common (‘of damp places and riversides’).
The above picture is taken (internet) from a German 19th century ‘herbal’ published by Franz Eugen Kohler (1834-1879) but written by number of authors including Herman Adolph Kohler, an exact contemporary of F.E.K.
At some point the plant was introduced into U.S.A. resulting in the State of Washington, for example, declaring it a ‘Noxious Weed’, making it a criminal offence to knowingly sow or distribute it. The equivalent term in Britain is ‘Pernicious Plant’. Usually the reason for such a definition is that they are poisonous to farm animals or humans or both. However, some poisonous plants are not so defined and some are defined as pernicious because, left unchecked, they smother-out all other plants.
Apparently cow parsley was also historically known by the sinister term ‘mother-die’, possibly because the carrot-like roots are semi-poisonous. Cow parsley is an ‘umbellifer’, that is a plant whose flower heads form ‘umbels’, clusters of small white flowers which together form an umbrella like shape. Other umbellifers are poisonous, particularly hemlock, the sap of which is said to have been the preferred poison of the Romans.
(Will get back to clay banks soon).