A new species Begonia siccacaudata is described. It belongs to the sect. Petermannia but is distinguished from other species by being stemless with a short fleshy rhizome. The female flowers are solitary, the male flowers are borne on a many-flowered thyrsoid inflorescence of a type not yet described within the genus. The epithet siccacaudata refers to the axes of the inflorescences which persist for a long time after dying off.