Joseph Martin Neumayer (1791–1840) was a dedicated naturalist who played a key role in documenting the flora of southern Dalmatia in the early 19th century. Through systematic fieldwork from the Dalmatian coast to inland mountains, as well as the islands, Neumayer collected plant specimens across diverse habitats, ranging from sea level to high altitudes. He collaborated closely with Roberto Visiani, sending well-documented herbarium material that contributed to his Flora Dalmatica and facilitated the description of seventeen taxa new to science. Neumayer's correspondence reveals his commitment to meticulous collection, identification, and knowledge exchange, as well as the practical challenges of field research in a malarial, rugged, and politically complex region. Analysis of preserved specimens indicates that some of the species Neumayer collected remain rare in the Croatian flora today. His work exemplifies the crucial link between local collectors and established botanists in advancing 19th-century Mediterranean botanical knowledge.