SummaryIn 1862, Charles Darwin published his landmark study on the different forms of flower in Primula; he coined the term distyly and subsequently expanded his studies to other species, including those with tristyly. Darwin is widely recognized as the first to study pin and thrum flowers in Primula, and to provide an explanation for the functional significance of the two floral morphs. Our laboratory is pursuing the genes that underpin floral heteromorphy in Primula, work influenced by Darwin's observations. One day, while appreciating a print of Primula vulgaris from William Curtis’ Flora Londinensis, I was struck by the fact that I was looking at images of dimorphic Primula flowers captured in a late‐1700s copper‐plate engraving that predated Darwin's observations by over 70 yr. This realization triggered a journey into archives of botanical texts, herbals and florilegia from the 16th to 19th Centuries, and correspondence archives, in search of earlier documents that could have influenced Darwin and the origins of an idea. Darwin was not the first to observe floral heteromorphy in Primula, but he was the first to realize the significance of the two floral morphs. Darwin's insight and exposition of purpose have underpinned all consequent work on the subject. Contents Summary 39 I. Introduction – the germination of an idea 39 II. Developments since Darwin 40 III. The evolution of Darwin's thinking on heterostyly 41 IV. Influences on Darwin's thinking 43 V. Darwin and the historical landscape of botanical illustration 45 VI. The historical work cited in Darwin's Different Forms of Flowers book 46 VII. The insights of Clusius and de Reneaulme and the influence of Linnaean thinking 47 Acknowledgements 48 References 49