James Cullen has been a professional plant taxonomist for over 50 years, working particularly on the classification and identification of plants in cultivation (especially Rhododendron) at Liverpool and Edinburgh Universities, at the Royal Botanic Garden, Edinburgh, and in Cambridge. With the late Dr S. M. Walters, he was the initiator of the first edition of The European Garden Flora and is responsible for two spin-offs, The Orchid Book (1992) and Manual of North European Garden Plants (2001).