Asa Gray was an American botanist best known as an nineteenth century authority on botanical taxonomy and a pioneer in plant geography. He was a strong supporter of Charles Darwin and his theory of natural selection.

Gray was born on November 18, 1810 in Sauquoit, New York. He attended Fairfield Medical School where he studied medicine. Subsequent to graduation, he briefly practiced medicine (1831-1832), then taught science at a Utica, New York high school while collecting plants and teaching himself botany. In 1934 he met John Torrey, a chemistry professor at the College of Physicians and Surgeons, New York. The two collaborated on Torrey and Gray's Flora of North America (1838-43); this was expanded and published as volume I of the Synoptical Flora of North America in 1878. Gray worked for a year in 1835 as librarian and curator of the New York Lyceum of Natural History. In 1836, he planned to join the United States Exploring Expedition as a botanist but he resigned before sailing due to frustration with delays. In 1838, Gray accepted a position at the University of Michigan, Ann Arbor Professor of Natural History and spent a year in Europe purchasing books for the university library, meeting botanists and studying American plants in European herbaria. In 1842, he accepted a position as Professor of Natural History at Harvard University, specializing in botany, a post he retained for 31 years until his retirement in 1873. Harvard named its botanical garden and herbarium which houses Gray's priceless collections of books and plants donated to the university after him. Gray died in Cambridge, Massachusetts on January 30, 1888.

Gray's career was highlighted by his relationship with Charles Darwin of whom he was a strong supporter. Using Darwin's theory of natural selection which Darwin shared with Gray in 1857 two years before the publication of Darwin's On The Origin of the Species, Gray explained the geographical distribution of flora occurring in Japan, northern and eastern America and Europe and theorized that all were descendents of circumboreal flora carried southward by glaciation during the Pleistocene era.

Gray published several hundred collected works, the best known of which was his Manual of the Botany of the Northern United States, from New England to Wisconsin and South to Ohio and Pennsylvania Inclusive (1848), also known as Gray's Manual . This comprehensive text helped establish systematic classification of botany in the United States.