1. Darwin, C. On the Various Contrivances by which British and Foreign Orchids are Fertilised by Insects (Murray, London, 1862).
2. Darwin, C. On the Origin of Species (Murray, London, 1859).
3. Rothschild, L. W. & Jordan, K. Novit. zool. 9 (suppl.), 1–972 (1903).
4. Nilsson, L. A., Jonsson, L., Rason, L. & Randrianjohany, E. Biol. J. Linn. Soc. Lond. 26, 1–19 (1985).
5. Nilsson, L. A. Bot. Notiser 131, 35–51 (1978).