“A case to which no parallel exists”: The influence of Darwin's Different Forms of Flowers

• Premise of the study: Research on the subject of heterostyly is often traced back to 1877 when Charles Darwin published the landmark book The Different Forms of Flowers on Plants of the Same Species . This book synthesized heterostyly research at the time, much of which Darwin conducted, and it continues to be a major contribution to the study of the breeding system. In this book, Darwin discussed the ecology, morph‐specific differences, self‐ and intramorph‐incompatibility, evolution and origin, and floral development of heterostyly. Many of the hypotheses he proposed have been and continue to be tested. • Key results: Throughout the 20 th and 21 st centuries, researchers have continued to identify new and different morph‐specific floral characters, discover the mechanisms that underlie heteromorphic self‐incompatibility, use phylogenies to examine the evolution of heterostyly, and determine novel floral developmental patterns in heterostylous species. From all of these studies, we have learned a great deal about the function, evolution, and development of heterostyly. • Conclusions: However, almost 150 years after Darwin's publications on the subject of heterostyly, we still have a great deal to learn concerning the breeding system, and new technologies and techniques are allowing for new advances in heterostyly research to occur.