William Trelease (February 22, 1857 – January 1, 1945) was an American botanist, entomologist, explorer, writer and educator.
He was Engelmann professor of botany at Washington University in St. Louis from 1885 to 1913, and appointed director of the Missouri Botanical Garden from 1889 to 1912.
[6] From 1913 to 1926 he was professor of botany and head of department at the University of Illinois.
Trelease was amongst the scientists on the two-month expedition to Alaska led by Edward Henry Harriman in 1899.
His work on the Piperaceae of Northern South America, left unfinished at his death, was completed by his student Truman G.