Geesink, R. 1., Leeuwenberg, A. J. M. 1., Ridsdale, C. E. 1., & Veldkamp, J. F. 1. (1981). Thonner's analytical key to the families of flowering plants. Wageningen: PUDOC, Centre for Agricultural Publishing and Documentation.
Chicago Style CitationGeesink, Robert 1945-1992, Antonius Josephus Maria 1930-2010 Leeuwenberg, Colin Ernest 1944-2017 Ridsdale, and Jan Frederik 1941- Veldkamp. Thonner's Analytical Key to the Families of Flowering Plants. Wageningen: PUDOC, Centre for Agricultural Publishing and Documentation, 1981.
MLA CitationGeesink, Robert 1945-1992, Antonius Josephus Maria 1930-2010 Leeuwenberg, Colin Ernest 1944-2017 Ridsdale, and Jan Frederik 1941- Veldkamp. Thonner's Analytical Key to the Families of Flowering Plants. Wageningen: PUDOC, Centre for Agricultural Publishing and Documentation, 1981.