Peter Hamilton Raven (June 13, 1936 – April 25, 2026) was an American botanist, environmentalist, and the longtime director and president of the Missouri Botanical Garden.
Early life On June 13, 1936, Raven was born in Shanghai, China, to American parents, Walter Francis Raven and Isabelle Marion Breen. His father's uncle Frank Jay Raven was, for a time, one of the wealthiest Americans in China but was later jailed in a banking scandal. That incident and Japanese aggression in China led the Raven family to return to San Francisco, California, in the late 1930s.
Raven became interested in beetles and plants from an early age, becoming a member of the California Academy of Sciences and the Sierra Club while still a youth. He went on to graduate with a BSc in biology from the University of California, Berkeley, in 1957 and a Ph.D. in botany from the University of California, Los Angeles, in 1960.
Career After teaching at Stanford University, Raven went on to become Director of the Missouri Botanical Garden in 1971. In 2006, his position was renamed President and Director. Raven announced his plans to retire in 2011, to coincide with his 75th birthday and his 40th year at the garden. Peter Wyse Jackson was appointed Raven's successor at the Missouri Botanical Garden in September 2010.
Raven is possibly best known for his work "Butterflies and Plants: A Study in Coevolution", published in the journal Evolution in 1964, which he coauthored with Paul R. Ehrlich. Since then he has authored numerous scientific and popular papers, many on the evening primrose family, Onagraceae. Raven is also an author of the widely used textbook Biology of Plants, now in its eighth edition, coauthored with Ray F. Evert and Susan E. Eichhorn (both of University of Wisconsin–Madison).
He was a frequent speaker on the need for biodiversity and species conservation.
In 2000, the American Society of Plant Taxonomists established the Peter Raven Award in his honor to be conferred to authors with outstanding contributions to plant taxonomy and "for exceptional efforts at outreach to non-scientists".
Raven served on the advisory council of CRDF Global. He served on the board of trustees for Science Service, now known as Society for Science, from 1993 to 1996.
Research Raven published more than 700 articles, books and monographs covering topics in evolution, taxonomy and systematics, biogeography, coevolution, plant conservation, ethnobotany, and public policy, including several text books.
During his early years he was associated with and led Sierra Club outings for several weeks at a time, after which he published "Base Camp Reports." Published from 1950 to 1956, these reports covered a wide range of subjects, including plant lists, insects, and ecology. His first such report, at the age of 14, summarized 506 plant collections representing 337 species collected in the Sierra Nevada Mountains in Inyo and Fresno Counties. G. Ledyard Stebbins was a counselor on this particular trip, identified by Raven as Prof. G. L. "Led" Stebbins.
During this time he also published on new weed species and other plants found in and around San Francisco as well as the Sierra Nevada Mountains.
In 1950, Raven, at the age of 14, had collected a plant called Clarkia rubicunda. In the early 1950s, in the course of revising the genus Clarkia Harlan Lewis and his wife Margaret Lewis discovered the herbarium specimen collected by Raven. They visited him in 1952 when he was 16, and wanted to know where the collection was made. Lewis eventually located the new species, and in 1958 Lewis and Raven published a botanical description of this plant, called C. franciscana, which was morphologically very closely related to C. rubicunda and C. amoena.
Many of Raven's early botanical and entomological collections are housed at the California Academy of Sciences herbarium (CAS).https://www.wikidata.org/wiki/Q139970722 His approximately 45,000 collections span seven decades from the 1950s through to the 2010s, with the bulk collected from the 1950s to the 1970s, and they are deposited in over 200 institutions.
Evolution While a graduate student at the University of California, Los Angeles, Raven and Harlan Lewis published a major paper in 1958 on the evolution of C. franciscana, and generalized to what was by then a general a pattern of speciation in Clarkia. They concluded that C. franciscana had evolved from Clarkia rubicunda; and they asserted that C. franciscana's origin mirrored a recurring theme in Clarkia of a derived species showing a close morphological similarity to a parental species, the derived species being geographically proximal, but differing from the parent by chromosomal differences and showing interspecific sterility. Further, they hypothesized that such speciation in Clarkia was rapid and perhaps occurred within the last 12,000 years.
Additionally, they hypothesized that this rapid mode of speciation seen in Clarkia was analogous to a mode of speciation known as quantum evolution.
Following his early publication in 1958 on evolution of C. franciscana, Raven went on to publish many papers on evolutionary topics. While at Stanford University, with Paul R. Ehrlich, he coined the term coevolution after a 1964 review of butterflies and their food plants.
In a 1969 paper Ehrlich and Raven were also critical of the idea that the definition of species as advocated by Ernst Mayr, Theodosius Dobzhansky, and G. Ledyard Stebbins had very little meaning for plants.
In 1978, Sussman and Raven advanced the idea that nonflying mammals, such as primates and marsupials, could have been significant pollinators but were outcompeted by nectar-feeding birds and bats. Any coevolved relationships between flowering plant species and non-flying mammal pollinators that persist at the present would appear to be "living fossils, which have a great deal to tell us about the evolution of both the mammals, including some of our antecedents, and of the flowering plants."
Raven wrote a review of the plant population data as of 1979, and identified several themes that he felt had potential for future research, including the above theme of the species problem. He went on to assert that developmental biology would be more important in the future He advocated another theme, that being that funding should be provided for study on a few species rather than spread amongst many in order to solve population biology problems:
In 1980, Raven continued discussing problems associated with defining species in plants. He discussed the widespread ability of plant species to hybridize, especially in perennial plants, and the historical observations of such back to 1717. He used as examples of perennial plants in the genera Epilobium, Scaevola, Bidens, and Ceanothus as examples of plants that appeared to use hybridization as a means to adapting to new environments. He stated "If the hybrids are particularly favored in specific ecological situations, asexual reproduction, polyploidy, or simply autogamy may favor the perpetuation of specific genotypes through a narrowing of the spectrum of genetic recombination characteristic of the population. No general conclusions about the most appropriate way to treat these populations taxonomically appear to be possible." In annual plants, using examples from Clarkia, he asserted that several species of Clarkia often occur sympatrically, yet hybrids are very rare in the wild," and that much of the sterility is due to chromosomal repatterning between species."
In 1980, Raven and coauthors reviewed the literature concerning fungal symbiosis in vascular plants. They reviewed two kinds of fungal-plant associations: ectomycorrhizal and endomycorrhizal. They reported that endomycorrhizal fungi, which penetrate plant cells, are found in 80% of all vascular plants, including ferns, gymnosperms, and angiosperms, and are found in forests of high species richness. On the other hand, ectomycorrhizal fungi, which do not penetrate plant cells, 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 the origin of the Cordilleran flora, a region bounded by the east slope of the Sierra Nevada and Transverse Ranges and Peninsular Ranges of California to the eastern front of the Rocky Mountains, north to the Snake River Plain-western Wyoming, and south to central Arizona-New Mexico.