Willis Linn Jepson (August 19, 1867 in Little Oak Ranch, near Vacaville, California – November 7, 1946 in Berkeley, California) is known as California's most distinguished early botanist. He graduated from the University of California in 1889, and become a UC professor in botany, a botanical writer, and a conservationist.
Jepson became interested in botany as a boy and explored the adjacent San Francisco Bay Area regions. He had come in contact with various botanists before he entered college.
In 1892, Jepson was 25 years old when he, John Muir, and Warren Olney formed the Sierra Club, in Olney's law office in San Francisco.
From 1895 to 1898 Jepson served as instructor, and carried on research at UC Berkeley, Cornell (1895) and Harvard (1896-97). He received his Ph.D. degree at University of California, Berkeley in 1899.
He was made assistant professor in 1899, associate professor in 1911, professor in 1918, and professor emeritus in 1937. He was a Professor of Botany at UC Berkeley for four decades, thus his entire career was identified with the University of California.
Jepson wrote at least 11 books during his lifetime, with two focused on California's trees. His works include A Flora of California (1909), The Trees of California (1909); and the major A Manual of the Flowering Plants of California (1925), predecessor of The Jepson Manual (1993).
His specimens, extensive archives and fieldbooks are housed in the University and Jepson Herbaria libraries and archives. Most of his specimens from California have been databased in the The Jepson Online Interchange for California Floristics − Jepson eFlora (TJM2) and form a multi-institutional Consortium of California Herbaria database.