Assessing the potential of medicinal plants- Where to start M. Bannayan Ferdowsi University of Mashhad, Faculty of Agriculture, P.O. Box 91775-1163, Mashhad Although there are over 350 000 plant species, fewer than 20 `major' crop species provide for most human food needs. Within the rest of the plant kingdom there remain many hundreds of underutilized food crops that have been grown locally for centuries and which contribute to the food security of the world's poorest people. In poor and impoverished regions of the world there are plants that have survived despite research and despite science. This is our chance to find out what those plants would be like as crops for the future — in climates of the future. With focussed scientific efforts applied to unconventional crops we can do things that will make them more valuable, more useful and more popular. Many of these crops are cultivated in hostile, tropical environments by small-scale farmers without access to irrigation or fertilizers and with little guidance on improved practices. Because the production and improvement of most underutilized crops have been ignored or actively discouraged by agricultural scientists, breeders and funding agencies, any attempts to improve their germplasm or management rely on local knowledge and initiative. There are few examples of a multidisciplinary research effort on an underutilized crop and no methodological framework that can be applied across a range of underutilized species. Simulation models are robust tools to guide our understanding of how a system responds to a given set of conditions. Crop simulation models are increasingly being used in agriculture to estimate production potentials, design plant ideotypes, transfer agrotechnologies, assist strategic and tactical decisions, forecast real time yields and establish research priorities. Although there are growth simulation models for a range of major crops, there have been few attempts to develop models for underutilised species for which the factors controlling growth and development are not well understood and the general literature is sparse. A major objective for developing BAMnut was to provide a means of integrating our preliminary understanding of the dynamics of crop growth as influenced by soil moisture and environmental variables. This allows the agro-ecological potential and resource requirements of the crop to be established. In particular, because BAMnut is a processbased model, it allows predictions of crop growth and yield to be generated and matched with current and potential production environments beyond those used in the development of the original model.