The concept of this book has taken some decades to acquire a definite shape. About thirty years ago I started attending the so-called pre-identification sessions of the then director of the Rijksherbarium, Prof. C.G.G.J, van Steenis († 14 May 1986) and Dr. R.C. Bakhuizen van den Brink Jr. († 1 May 1987), the co-author of the ‘Flora of Java’ (Backer & Bakhuizen van den Brink, 1963-1968). They spent one day a week going through all incoming material, checking the identifications on the labels and identifying unnamed specimens. The plants not recognized at first sight were put aside for further scrutiny. It was usually Rein Bakhuizen who enjoyed cracking the hard nuts. In the case of identifying trees Van Steenis and Bakhuizen very often relied on Mr. F.H. Hildebrand († 7 July 1975), who, as a former forester of the Forest Research Institute in Bogor, had a vast knowledge of Malesian tree species. These sessions were quite unforgettable, although I must admit that the first few years were pretty rough. The two went through the piles of material like a whirlwind, each trying to beat the other in naming the plants. The only break I had was when they had an argument, or when I put in a silly question, such as: “How do you know?”