Asa Gray (November 18, 1810 – January 30, 1888) was an influential American botanist and collaborator of Charles Darwin. He was instrumental in unifying the taxonomic knowledge of the plants of North America.
Of Gray's many works on botany, the most popular was his Manual of the Botany of the Northern United States, from New England to Wisconsin and South to Ohio and Pennsylvania Inclusive. This book, known simply as Gray's Manual, has gone through a number of editions, and remains a standard in the field.
In 1842, Gray became Fisher professor of natural history at Harvard University. Through the donation of an immense book and plant collection numbering in the thousands, he effectively created the botany department at Harvard; the Gray Herbarium is named after him.
Corresponding with Darwin, Gray was helpful in providing information for the development of Darwin's theory on The Origin of Species. He was a staunch supporter of Darwin in America, and collected together a number of his own writings to produce an influential book, Darwiniana.
The standard botanical author abbreviation A. Gray is applied to plants described by Gray.