Five British Papaver spp. are described: P. rhoeas L., P. dubium L., P. lecoqii Lamotte, P. argemone L., and P. hybridum L. Details are given of morphological variation, geographical and altitudinal distribution, habitat preferences, associated flora, response to biotic factors, gregariousness, reproduction and seed dispersal, seed germination, chromosome numbers, hybridization, floral biology, insect visitors, parasites and diseases, etc.