This introduction is one of many similar looking yellow crucifers which grow at the side of the road in spring. It isn't easy to separate from B. napus (Oilseed rape) which is an escape from cultivation and frequently grown in these parts but which has usually much greyer and buds which grow higher than the flowers. There are various sub species of B rapa which I doubt I could identify.

Near Shotton North Wales 1st March 2005

Added on 3rd March 2005, updated 4th November 2008, updated 5th March 2010, updated Se3 27th April 2010