| August Wilhelm Eichler | |
| Birth Place: | Neukirchen, Hesse |
| Death Place: | Berlin |
| Nationality: | German |
| Field: | Botany, Plant taxonomy |
| Author Abbrev Bot: | Eichler |
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.His author abbreviation in botany is Eichler.
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. In 1872 he received an appointment at the University of Kiel, where he remained until 1878 when he became director of the herbarium at the University of Berlin. He died in Berlin on March 2, 1887, of leukaemia.
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.
The Eichler System divided the plant kingdom into non-floral plants (Cryptogamae) and floral plants (Phanerogamae). It was the first to accept the concept of evolution and therefore also the first to be considered phylogenetic. Moreover, Eichler was the first taxonomist to separate the Phanerogamae into Angiosperms and Gymnosperms and the former into Monocotyledonae and Dicotyledonae.
The Eichler system was the foundation for Adolf Engler's System and was widely accepted in Europe and other parts of the world.