Mårten Magnus Wilhelm Brenner (1843–1930) was a non-professional Finnish botanist who published 220 articles or notes. Brenner worked on East Fennoscandian vascular plants (the territory of present-day Finland and adjacent Russia). He validly published ca. 833 new taxa, especially in genus Hieracium (including Pilosella), and introduced 56 names as nomina nuda. Brenner had no concept of type specimens and therefore all his plant taxa need typification, and 151 of those are lectotypified here. In this paper, nomina nuda and the taxa whose type material was not found are also listed, except those of the apomictic genera Hieracium and Taraxacum. Many of Brenner's new taxa are forms and varieties, generally not recognised nowadays. Many of his taxa were based on single or few specimens and therefore were characterised by local distributions, whereas some include ample original material. Finnish botanists generally ignored Brenner's contributions to taxonomy. However, 11 species of Hieracium, 20 of Taraxacum and Euphrasia stricta var. tenuis (Brenner) Jalas are currently recognised, and recently also E. wettsteinii var. botniensium (Brenner) Piirainen. Together Brenner's type collection treated here consists of 254 sheets (Hieracium and Taraxacum excluded), deposited at the Botanical Museum (H), Finnish Museum of Natural History, University of Helsinki, Finland.