Peter Hamilton Raven (born June 13, 1936) is an American botanist and environmentalist, notable as the longtime director, now President Emeritus, of the Missouri Botanical Garden.

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.

[3][4] That incident and Japanese aggression in China led the Raven family to return to San Francisco, California, in the late 1930s.

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.

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).

[5] 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."

[15] 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.

[16] In 1978 Sussman and Raven[17] 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.

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.

[12][5] In 1988 he published a review of the Onagraceae, covering its taxonomy, evolution, cytogenetics, anatomy, breeding systems, and geographic distribution.

In 1974, with Daniel I. Axelrod, Raven published an extensive article on plant and animal biogeography in the context of plate tectonics.

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.

[27] In 1996 Raven, Axelrod, and Al-Shehbaz wrote a paper on the history of the modern flora of China, Europe, and the continental United States.

Second, there is an unbroken gradient of vegetation from the tropical rain forest to "boreal coniferous forests that has persisted and afforded habitats characterized by equable climates during the last 15 million years, when massive extinctions were taking place elsewhere in the Northern Hemisphere...such continuity is interrupted in North America by the Gulf of Mexico and in Europe by the Alps, the Mediterranean, and the Sahara Desert."

The third reason was due to the impact of the Indian subcontinent with Asia starting 50 million years ago, making a "highly dissected, elevated geography."

[38][39][40][41] Raven (along with Dennis E. Breedlove) was a collaborator on a team led by Brent Berlin that published a seminal work on the classification of plants by the Tzeltal Mayan-speaking people of Highland Chiapas.