Motivated by his interest in botanical history and taxonomy, Stearn devoted a considerable part of his output to botanical bibliography, including numerous papers and catalogues establishing the exact publication dates of books on natural history, particularly from the early nineteenth century, including William Herbert's work on Amaryllidaceae (1821, 1837) and complete bibliographies of botanists such as John Gilmour (1989). At the RHS library he transformed the minimalist card indexing by introducing British Museum rules and adding extensive bibliographic information. He quickly realised that one of the major deficits in contemporary taxonomic nomenclature was a lack of precise dates of all the names, and set about rectifying this over a fifteen-year period, resulting in 86 publications, which was a major step in stabilising nomenclature. The importance of this lay in the rules of botanical nomenclature, which gives botanical names priority based on dates of publication. He considered his most important contribution in this regard to be his elucidation of the dating of the early 19th century collection of studies of Canary Islands flora by Webb and Berthelot (1836–1850). Another important work from this period was on Ventenat's "Jardin de la Malmaison" (1803–1804), also published in the new "Journal of the Society for the Bibliography of Natural History". In a number of instances his contributions to others' work went unacknowledged, particularly when he was younger, even though his introductions (often with the title "Revised and enlarged by W. T. Stearn") could be as lengthy as the texts they preceded. His contributions to botanical bibliography and in particular the correct interpretation of historical texts from Linnaeus to Arber are considered of central importance to the field of taxonomy.