Acknowledgements: We are grateful to the Directors/ Curators of the following herbaria for herbarium and library facilities: BM, K, KUH and RAW. It is a matter of pleasure to express our gratitude to Professor J. Leonard for offering critical and helpful comments on our manuscript. The author wishes to express her gratitude to Brigadier Mukhtar Ahmad, President, Houbara Foundation for facilitating the survey of the relevant area. We gratefully acknowledge financial support for this publication from the Andrew W. Mellon Foundation and National Science Foundation (DEB 0103783), Washington, U.S.A. obtained through the Missouri Botanical Garden, St. Louis, U.S.A. We are grateful to Professor P. H. Raven of the Missouri Botanical Garden for his assistance in securing this support. Grateful thanks are due to Professor Zafar Saied Saify, Vice-Chancellor, University of Karachi and Professor M. Qaiser, Chairman, Department of Botany, University of Karachi for providing working facilities to the project and for their understanding and encouragement.