John Tucker, professor emeritus of botany at the University of California, Davis, and an internationally recognized oak expert, died July 5 at Sutter Davis Hospital from complications of a stroke. He was 92.

An authority on the classification and naming of plants, particularly oaks, he served for 39 years as director of the J.M. Tucker Herbarium, now part of the UC Davis Center for Plant Diversity herbarium, a collection of more than 250,000 dried plant specimens. He also served as director of the UC Davis Arboretum for 12 years.

Born on Jan. 7, 1916, in Amity, Ore., Tucker grew up in Santa Barbara, Calif. He credited Boy Scout hikes and campouts in California's Central Coast mountains with sparking his interest in native wild plants, particularly trees.

After graduating from Santa Barbara High School in 1934, he considered a career in forestry. He wrote in later years, however, that the director of the Santa Barbara Botanical Gardens had convinced him that he "was a botanist, not a forester."

Taking that advice, Tucker gathered up his savings and enrolled in UC Berkeley, where he earned a bachelor's degree and a doctorate, both in botany, in 1940 and 1950, respectively.

While at Berkeley, he met his future wife, Katrine June Petersen. The couple married in 1942 and later had three children.

While still a graduate student at UC Berkeley, Tucker was hired as director of what was then UC Davis' Botany Department Herbarium. At that time the herbarium comprised 9,400 specimens in just six wooden cases.

In 1951, he initiated an exchange program for trading extra specimens with other institutions. Under his leadership, the collection of weeds, California flora and oaks expanded dramatically, and the herbarium developed into a global resource.

Today, the herbarium is frequented each year by hundreds of people who use its library, view the preserved specimens and identify their own plant specimens. These visitors include UC Davis students, and faculty and staff members, as well as visiting university researchers, government biologists, private consultants and members of the public.

Upon Tucker's retirement in 1986, the Botany Department Herbarium was officially named the J.M. Tucker Herbarium.

In addition to the herbarium's archive of preserved plant specimens, Tucker also devoted his energy and expertise to a living oak collection. In 1962, he established an oak grove near the western end of the UC Davis Arboretum, planting acorns that he had collected from around the world.

Today the arboretum is home to 574 oak trees, including a number of native California oak species. This group of oaks is particularly important because it contains the greatest taxonomic diversity of any known oak collection and includes 17 oak varieties not found in any other collection.

"John was a leader in the study of the variation within oak populations and hybridization between populations, who generously shared his oak identification skills," said Ellen Dean, current curator of the UC Davis Center for Plant Diversity. "He was also a committed director of both the UC Davis Arboretum and the John Tucker Herbarium, and a mentor to thousands of UC Davis students.

"When alums of UC Davis approach me to tell me about their experience in the old botany department, more often than not, they tell me about how wonderful it was to take John's plant taxonomy or poisonous plants classes."

In retirement, he continued to give of his time and resources to the university. In 2001, he contributed $500,000 to support the growth and development of both the herbarium and arboretum on campus.

Tucker once wrote that oaks fascinated him because they were so challenging to classify. He noted that individual species are highly variable, and closely related oak species are often quite difficult to distinguish from each other. As a researcher, he was particularly interested in the tendency of oak species to hybridize, crossing in nature to create new species that he found to be "interesting but very confusing hybrid complexes."

In addition to his research activities, he taught a broad spectrum of undergraduate and graduate courses, including classes on general botany, plant systematics and poisonous plant identification.

Away from campus, Tucker enjoyed keeping up on current events and was an avid reader, reading four to five newspapers every day. Duke Ellington and Count Basie were his favorite recording artists, and he occasionally attended Winton Marsalis concerts with his children. He also enjoyed attending football games between UC Berkeley and Stanford University with his nephew, Ernest Valenzuela.

During his career, Tucker received numerous honors and awards, including a Guggenheim Fellowship in 1955. He was selected as a fellow of the American Association for the Advancement of Science and the California Academy of Sciences.

He also was a member of the American Institute of Biological Sciences, American Society of Plant Taxonomists, Botanical Society of America, California Botanical Society, International Association for Plant Taxonomy, Sigma Xi honor society and Society for the Study of Evolution.

He was preceded in death by his wife; brother, Robert Tucker; and sisters, Viola Valenzuela and Helen Reid.

He is survived by his daughter, Carolyn Tucker, and son, Peter Tucker, both of Sacramento; sister Mary Kraft of Santa Barbara; brothers Glenn Tucker of Sonora, Ken Tucker and his wife, Shirley, of Santa Barbara, and Stanley Tucker and his wife, Marion, also of Santa Barbara. He also leaves his grandson, Carson Mack of Sacramento.

A memorial service in his honor is planned for 10 a.m. Saturday, Aug. 9, at the UC Davis University Club on Old Davis Road. The service will be followed by an informal luncheon.

In lieu of flowers, the family requests that memorial donations be made to either the UC Davis Foundation Herbarium Endowment in support of the J.M. Tucker Herbarium or the UC Regents J.M. Tucker Endowment in Support of the Arboretum's oak collection. Donations may be sent to: Allison Chilcott, CAES Dean's Office, 150 Mrak Hall, One Shields Ave., UC Davis, Davis, CA 95616.