August Wilhelm Eichler, also known under his Latinized name, Augustus Guilielmus Eichler (22 April 1839 – 2 March 1887), was a German botanist who developed a new system of classification of plants to reflect the concept of evolution.

Born in Neukirchen, Hesse, Eichler studied at the University of Marburg, Germany, and in 1871 became Professor of Botany at Technische Hochschule (Technical University) of Graz and director of the botanical garden in that city.

Eichler made important contributions to the study of the comparative structure of flowers (mainly on floral symmetry in his work Blütendiagramme).

He wrote extensively on the Coniferae, Cycadaceae and other plant groups of Brazil.

[3] Moreover, Eichler was the first taxonomist to separate the Phanerogamae into Angiosperms and Gymnosperms and the former into Monocotyledonae and Dicotyledonae.