Willi Giess made an enormous contribution to the collection of herbarium material in the "S.W.A. Herbarium" (now the National Herbarium of Namibia). Of the approximately 73 000 specimens in the present-day collection, 18 570 specimens were collected by him personally, often with other scientists like O. Volk, D. van Vuuren, B. de Winter, and in collaboration with H. Merxmüler. These specimens were all collected in triplicate, often even in quadruplicate. Anybody who has ever collected seriously for a herbarium will appreciate the amount of work involved in such a collection. Even today, the Giess-specimens, with their carefully typed or hand-written data labels, are often the best and neatest to be found in the collection of the National Herbarium of Namibia.