Elmer Ivan Applegate (March 31, 1867 – November 16, 1949) was an American botanist.
Between 1896 and 1898, he spent 5 months a year, under supervision of Frederick Coville of the US Department of Agriculture, where he did plant surveys in the Cascade Mountains, that can range from Klamath Falls to Portland.
Between 1928 and 1938 he was appointed as an honorary acting director of the Dudley Herbarium, at Stanford University.
In 1940, he was awarded an honorary Doctor of Science degree from Oregon State College.
She was a niece of Peter Skene Ogden, a Hudson's Bay Company explorer.