Raven's Ph.D. thesis was on a genus within the Onagraceae, and his interest on the evolution of plants within this family as well as the Myrtales runs through his entire career. In 1988 he published a review of the Onagraceae, covering its taxonomy, evolution, cytogenetics, anatomy, breeding systems, and geographic distribution. He asserted that the family was the best known plant family of its size, and proposed that further studies of the family would be useful in understanding of "variation and evolution of plants in the future."