Charlock (Brassica arvensis)
Now known as Sinapis arvensis; also formerly called Brassica kaber. A common weed along roadsides and in fields. The larger flowers easily distinguish it from the other wlid mustards.
Gray describes the genus and the species:
BRASSICA [Tourn.] L. MUSTARD. TURNIP
Annuals or biennials, with yellow flowers. Lower leaves mostly lyrate, incised, or pinnatifid. (The Latin name of the Cabbage.)
B. ARVENSIS (L.) Ktze. (CHARLOCK.) Knotty pods fully one third occupied by a stout 2-cdged beak; upper leaves rhombic, scarcely petioled, merely toothed; fruiting pedicels short, thick; pods smooth or rarely bristly. 4 cm. long. (B. Sinapistrum Boiss.; Sinapis arvensis L.) Noxious weed in grainfields, etc. (Nat. from Eu.)