A morphologically distinct group of 10 species within the Begonia L. sect. Eupetalum (Lindl.) A. DC. is identified and informally named as the B. octopetala L'Hér. species group. Two new species of Begonia (Begoniaceae) are described and illustrated from this group. The new species B. pseudopleiopetala Tebbitt is based upon type material collected from the Cajamarca region in Peru and is also known from the Piura region of Peru; the second new species B. marinae Tebbitt is based upon type material collected from the Santa Cruz Department in Bolivia and is also known from La Paz, Chuquisaca, and Tarija departments, Bolivia, as well as the province of Salta in adjacent Argentina. A taxonomic synopsis of B. octopetala and a description of one additional species from this species group, B. pleiopetala A. DC., are also provided for comparison. Begonia gracillima A. DC. and B. tenuicaulis A. DC. are newly synonymized with B. pleiopetala. Lectotypes are provided for B. gracillima [= B. pleiopetala], B. pusilla A. DC. [= B. pleiopetala], B. tenuicaulis [= B. pleiopetala], and B. warburgiana Hieron. [= B. pleiopetala].