A rare plant register is a dynamic list of all the scarce and threatened plants in a county or vice-county together with details of all the most recent records for known sites for those plants. BSBI has produced a list of criteria and definitions that govern whether or not a species should be included in the register or not depending on conservation status, native status (locally) and number of known sites. Once available, the register helps makes sure that conservation practitioners and planners are aware of the presence of the threatened species in an area and can facilitate the monitoring of these species. Keeping the register up to date will be an ongoing project. A provisional list of candidate species is available here
Corn Marigold (Glebionis segetum) is listed as Vulnerable in the England Red List. It is, however, present in quite a few sites in Norfolk and its native status is sometimes debatable due to occasional inclusion in 'wildflower' seed mixes. It should be included in the rare plant register, but it is unlikely that all sites will be listed.
Ref. Stroh, P.A. et al, 2014, A Vascular Plant Red List for England, BSBI.