A new species of Begonia sect. Quadrilobaria from the Northwestern dry forest of Madagascar is described and illustrated with a line drawing. The new species is compared with morphologically similar species, B. bagotiana Humbert ex Keraudren & Bosser, B. bekopakensis Aymonin & Bosser and B. neoperrieri Humbert ex Keraudren & Bosser, and its distinctive characteristics are provided as well as a provisional extinction risk assessment.