The world’s smallest Begonia, Begonia elachista Moonlight & Tebbitt sp. nov., is described and illustrated from a limestone outcrop in the Amazonian lowlands of Pasco Region, Peru. It is placed within the newly described, monotypic Begonia sect. Microtuberosa Moonlight & Tebbitt sect. nov. and the phylogenetic affinities of the section are examined. Begonia elachista sp. nov. is considered Critically Endangered under the International Union for the Conservation of Nature (IUCN) criteria.
Begonia, sectional classification, limestone endemics, Peru, Amazonia.