Katherine Esau (3 April 1898 – 4 June 1997) was a pioneering German-American botanist who studied plant anatomy and the effects of viruses.

In 1989, Esau received the National Medal of Science "In recognition of her distinguished service to the American community of plant biologists, and for the excellence of her pioneering research, both basic and applied, on plant structure and development, which has spanned more than six decades; for her superlative performance as an educator, in the classroom and through her books; for the encouragement and inspiration she has given to a legion of young, aspiring plant biologists; and for providing a special role model for women in science."

Peter Raven 'Director of Anatomy and Morphology' of 'Missouri Botanical Garden' remembered that she absolutely dominated the field of plant Biology even at the age of 99.

[3] The family managed to escape by boarding a German troop train in Ekaterinoslav on 20 December 1918, reaching Berlin on 5 January 1919 after a two-week trip.

She studied farm management with Friedrich Aereboe [de] and plant breeding with geneticist Erwin Baur.

In 1923, she worked for a seed production ranch, raising and studying sugar beets in Oxnard, California.

[3] Since Davis did not grant graduate degrees at that time, she officially registered for the Ph.D. program through the University of California Berkeley.

This led to her focus on plant anatomy and especially phloem tissue that was the subject of her scientific career.

[10] While teaching at the University of California, Davis, she continued her research on viruses and specifically phloem, the food conducting tissue in plants.

Her papers are held by the Department of Special Collections in the Davidson Library at the University of California, Santa Barbara.

[4] Ray Evert, one of Esau's graduate students, says: "The book Plant Anatomy brought to life what previously had seemed to me to be a rather dull subject.

"[10] Esau did not seem to attach importance to the recognition accorded her, and she told David Russell, who compiled her oral history, "I don't know how I happened to be elected [for the National Medal of Science].

"[13] Many of Esau's publications are housed and available for loan from the Cornelius Herman Muller library at the University of California, Santa Barbara's Cheadle Center for Biodiversity and Ecological Restoration.