We are grateful to E. B. Walujo (LIPI, Cibinong Science Centre, BO), and M. Siregar and Hartutiningsih (LIPI, Bogor Botanic Gardens), for their support of our expeditions in Indonesia; to K. Armstrong, D. Girmansyah, M. Newman, A. Poulsen and H. Wiriadinata for providing plant material; to the horticulture staff at Bali Botanic Garden, Bogor Botanic Gardens, the Royal Botanic Garden Edinburgh and the Royal Botanic Gardens Glasgow for their expert care of the Begonia collections; to the curators of A, B, BM, BO, CEB, E, L, K, SING and WAG for allowing us access to herbarium material and living collections; and to A.N. Muellner, S. S. Renner, R. M. K. Saunders and an anonymous referee for their constructive comments on the manuscript. This research would not have been possible without the support of the Indonesian Ministry of Research and Technology (RISTEK) and Direktorat Jenderal Perlindungan Hutan dan Konservasi (DITJET PHKA). The funding of the first author's studies by the M. L. MacIntyre Trust, and support of two expeditions to Sulawesi in 2008 and 2009 by the Royal Horticultural Society, the Stanley Smith (UK) Horticultural Trust and the Systematics Association is gratefully acknowledged.