On the BSBI Literature Database you can search for botanical literature by genus. It is fairly comprehensive for publications on British & Irish plants in the second half of the 20th century.
Douglas Simpson’s comprehensive listing of sources of botanical information relating to the Britain and Ireland is now a scarce and valuable tome. It was scanned and digitised by Tim Rich and is made available here as a download. Abbrevations have been expanded to make it more readable.
Simpson, N.D. 1960 A Bibliographical Index of the British Flora. Privately printed, Bournemouth. Digitised and expanded by T.C.G. Rich, 2004.
>> Simpson’s Index