**Background:** This paper presents a comparative inventory of medicinal plant taxa and their uses by smallholder farming communities of four cultures (Lango, Acholi, Teso, Ethur) in the Aswa River catchment of northern Uganda, situated in the eastern Sudanian savanna parkland ecotype. The study was conducted before civil conflict and mass displacement disrupted inter-generational transmission of traditional technical knowledge. The WHO estimates up to 80% of the global population relies on plant compounds in primary healthcare, and 60% of Ugandans use traditional medicine, 90% of which is plant-based. The study aimed to document ethnobotanical use of medicinal plants by these four cultures at a historical moment before conflict disrupted knowledge transmission.
**Methods:** Following community consultations in four districts during 1999–2000, interviews were conducted with 112 holders of specialist knowledge on plants used as medicine. Each plant specimen was allocated a voucher number and identified by the Makerere University Herbarium. Use reports reflecting specific medicinal applications were compiled in aggregate to obtain a Relative Importance Index (RI) ranking. The commonality of medicinal taxa cited between each cultural interface was assessed by the Jaccard Index of Similarity, and the similarity of specific medicinal usage by taxon using Rahman’s Similarity Index. Data were triangulated by three rounds of secondary research including ethnobotanical publications, pharmacological studies, and phytochemical analyses.
**Key Results:** The data collected from 112 respondents (82 men, 30 women) comprise 280 medicinal use reports describing 263 applications for 62 medical conditions, citing 108 taxa from 44 botanical families. Fabaceae comprised 20% of all use reports. No earlier mention could be found to corroborate 72 use reports (27% of the total), representing medicinal indications as yet undocumented. The RI values ranged between 15 and 94%, with 13 taxa having RI values above 50%. Five taxa were ranked above 70%: Harrisonia abyssinica (RI 0.86), Lepistemon owariense (RI 0.79), Sarcocephalus latifolius (RI 0.71), Solanum incanum (RI 0.71), and Senna singueana (RI 0.71). The Jaccard Index ratios indicate the highest degree of similarity in plant taxa used as medicine (21%) between Lango and Teso cultures who share a common origin; however, Rahman's Similarity Index indicates the highest similarity of specific medicinal usage by taxon between Lango and Acholi (20.5%), who share a common language group through cultural assimilation. Plant parts used showed a strong preference for roots (about 60% of use reports), followed by leaves (over 23%). The most cited conditions were measles (41 use reports, 27 taxa), diarrhea (33 use reports, 21 taxa), and cough (28 use reports, 21 taxa).
**Clinical Implications:** The study provides a comprehensive inventory of medicinal plant use in a region where conventional medical services are largely inaccessible, with a 1:700 ratio of traditional healers to population versus 1:25,000 ratio of medical doctors. The high proportion (27%) of previously undocumented use reports suggests potential for pharmacological investigation, particularly for taxa with high RI values like Lepistemon owariense (RI 0.79) for which no earlier mention was found. The findings on measles treatment are clinically relevant given that national measles vaccination coverage was just 74% in 2002, leaving over a quarter of Ugandan children unprotected. Diarrhea, accounting for over 20% of child deaths in Uganda (global average 8.6%), was the highest-ranked malady in three of four cultures. The study also documents treatments for snakebite, which causes an estimated 32,000 annual deaths across sub-Saharan Africa, with antivenom supplies insufficient even at hospitals in northern Uganda. The results imply that cultural exchange and assimilation may be a greater driver of inter-cultural similarity of ethnopharmacological use of a given taxon compared to shared historical origins.