This first part of the flora treatment for the Cyperaceae occurring in the Democratic Republic of the Congo, Rwanda and Burundi provides general family-level information, a key to the 13 tribes occurring in this region, and deals with the first tribe, belonging to the subfamily Mapanioideae. The tribal classification follows that of Semmouri & al. (2019). Within the region dealt with by this Flora, 24 genera and around 400 species are present. The first tribe, Hypolytreae, is dealt with and comprises 2 genera and 14 species. Each species treatment comes with a full description, synonyms, data on their distribution ,habitat, vernacular names and uses, as well as references to additional literature and the citation of representative specimens. User-friendly keys to all genera and species are provided, along with 6 plates aiding in understanding Cyperaceae morphology and 12 detailed line drawings as well as 14 colour photographs to assist species recognition.