Sereno Watson (December 1, 1826 in East Windsor Hill, Connecticut – March 9, 1892 in Cambridge, Massachusetts) was an American botanist. Graduating from Yale in 1847 in Biology, he drifted through various occupations until, in California, he joined the Clarence King Expedition and eventually became its expedition botanist. Appointed by Asa Gray as assistant in the Gray Herbarium of Harvard University in 1873, he later became its curator, a position he maintained until his death. Watson was elected a Fellow of the American Academy of Arts and Sciences in 1874, and a member of the National Academy of Sciences in 1889.

The standard author abbreviation S.Watson is used to indicate this person as the author when citing a botanical name.