An up-to-date biography of Mihael Dimonie (1870-1935), an important Aromanian plant collector in the southern Balkan Peninsula, is presented. So far, he has been better known to linguists than to botanists on account of the Codex Dimonie and his contributions to Aromanian cultural heritage. His private herbarium collections were destroyed in two separate fires in 1917 and 1944, and only the numerous vouchers belonging to the Plantae Macedonicae series that had been commercially distributed remain. These specimens are available in several European and American herbaria and are a lasting testament to Dimonie's extensive collecting activities in what are today Albania, Bulgaria, Greece and North Macedonia. His collecting localities in the southern Balkans are indicated in a map. Seven names based on material collected by Dimonie and one based on material collected by Ignaz Dörfler are lectotypified and nomenclatural notes for six other taxa are presented. A preliminary list of taxa described (or partly described) from Dimonie's material includes at least 29 names. Citation: Pachschwöll C., Reich D. & Tan K. 2019: The botanical legacy of Mihael Dimonie (1870-1935), an almost forgotten plant collector in the southern Balkan Peninsula before the First World War. - Willdenowia 49: 257-279. doi: https://doi.org/10.3372/wi.49.49213 Version of record first published online on 29 August 2019 ahead of inclusion in August 2019 issue.