occur in forests of low species richness, are usually in temperate forests, or infertile soils of the tropics. Further, they hypothesized that ectomycorrhizal forests have expanded through the Middle Cretaceous at the expense of endomycorrhizal forests. 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." Biogeography Raven showed an early interest in plant disjunctions prior to the wide acceptance of plate tectonic theory of the late 1960s, and was an early adopter of plate tectonics in explaining plant disjunctions by the early 1970s. In 1963 Raven published a review of amphitropical distributions of plant species in North and South America. He divided species into three groups: biopolar or high-latitude species, temperate species, and desert species. In 1974, with Daniel I. Axelrod, Raven published an extensive article on plant and animal biogeography in the context of plate tectonics. They stated that the new plate tectonic theory "did not require any new modifications of previously established major principles of evolution...however there were new principles of biogeography..." In 1978, again with Axelrod, they published on the origin and complexity of Californian flora. They reviewed that the flora of California consisted of "northern, temperate elements and xeric, southern elements, and is characterized by a high degree of endemism." They proposed that the reasons for the large number of species in the state as well as the endemics is due to the favorable climate that has prevailed in California for most of the Tertiary, as well as the recent elevation of the Sierra Nevada and other ranges, together with: "The concomitant development of a cold off-shore current which ultimately resulted in the development of a mediterranean, summer-dry climate during the past million years...The endemics of California are a mixture of relicts and newly produced species...and it is the latter that have contributed most to the size of the flora and to the high proportion of endemism in it." Raven and Axelrod wrote a paper in 1985 on