May be you konw this references, but if is not the case, could help.

Dillehay, Tom (Ed). From Foraging to Farming in the Andes: New Perspectives on Food Production and Social Organization. Cambridge University Press, 2011

Morcote, Gaspar. Antiguos habitantes en ríos de aguas negras. Ecosistemas y cultivos en el interfluvio Amazonas - Putumayo, Colombia-Brasil, Bogotá: Universidad Nacional de Colombia- Instituto de Ciencias Naturales, 2008

Pearsall, Deborah. Plant domestication and the shift to agriculture in the Andes. In: Handbook of South American archaeology. Eds. H. Silverman & W. Isbell. Pp. 105-120. New York: Springer, 2008

Mora, Santiago. Agricultores, cazadores y recolectores: ¿lógicas y economías opuestas y complementarias?. In: Amazonía, pasado y presente de un territorio remoto. El ámbito, la historia y la cultura vista por antropólogos y arqueólogos. Pp. 59-80. Bogotá: Uniandes - Ceso, Fondo de Promoción de la Cultura del Banco Popular, 2006

Kennett, D. J. & K. Winterbalder (Eds.). Behavioral Ecology and the Transition to Agriculture. University of California Press, 2006

Thorpe, I. The Origins of Agriculture in Europpe. Routledge, 1996

May be you konw this references, but if is not the case, could help.

Dillehay, Tom (Ed). From Foraging to Farming in the Andes: New Perspectives on Food Production and Social Organization. Cambridge University Press, 2011

Morcote, Gaspar. Antiguos habitantes en ríos de aguas negras. Ecosistemas y cultivos en el interfluvio Amazonas - Putumayo, Colombia-Brasil, Bogotá: Universidad Nacional de Colombia- Instituto de Ciencias Naturales, 2008

Pearsall, Deborah. Plant domestication and the shift to agriculture in the Andes. In: Handbook of South American archaeology. Eds. H. Silverman & W. Isbell. Pp. 105-120. New York: Springer, 2008

Mora, Santiago. Agricultores, cazadores y recolectores: ¿lógicas y economías opuestas y complementarias?. In: Amazonía, pasado y presente de un territorio remoto. El ámbito, la historia y la cultura vista por antropólogos y arqueólogos. Pp. 59-80. Bogotá: Uniandes - Ceso, Fondo de Promoción de la Cultura del Banco Popular, 2006

Kennett, D. J. & K. Winterbalder (Eds.). Behavioral Ecology and the Transition to Agriculture. University of California Press, 2006

Thorpe, I. The Origins of Agriculture in Europpe. Routledge, 1996

At the risk of reiterating what is well-known, this thread would be incomplete without a mention of Richard MacNeish's classic diachronic, interdisciplinary study of a region in south-central Mexico: The Prehistory of the Tehuacan Valley (1967-1972). Volume 1 (of five) is dedicated to "Environment and subsistance." More recent research has added much information, but this massive contribution continues to be relevant for understanding the changing relationship of human populations to their environments.

On these studies, and MacNeish's contributions to research in other parts of the world, see: http://books.nap.edu/html/biomems/rmacneish.pdf

You are probably familiar with research in eastern North America, so at the risk of providing info you are already familiar with... The seeds of several weeds were collected and likely cultivated for some hundreds of years before the arrival of domesticated plants. In this case, "domesticated plants" refers to squash, beans and maize, and weedy plants include chenopodium, goosefoot, sumpweed and others, along with nuts, berries and other fruits. The debate about whether any of these weeds were domesticated, or to what degree they were domesticated, is ongoing, but there is very good evidence for extensive use of these weeds in prehistory.

Kristen Gremillion has a ResearchGate page that should provide all the basics for this region.

Some useful resources:

Gremillion, K. 2004 Seed Processing and the Origins of Food Production in Eastern North America. American Antiquity 69: 215-234.

Hart, J.P. (editor). 1999. Current Northeast Paleoethnobotany. The University of the State of New York, Albany, NY.

Smith, B.D. 1989. Origins of Agriculture in Eastern North America. Science 246:1566-1571.

Watson, P.J. and M.C. Kennedy. 1998. The Development of Horticulture in the Eastern Woodlands of North America: Women’s Role. In Reader in Gender Archaeology, edited by K. Hays-Gilpin and D.S. Whitley, pp. 173-190. Routledge, London.

Wymer, Dee Anne. 1996. The Ohio Hopewell Econiche: Human-Land Interaction in the Core Area. In A View From the Core: A Synthesis of Ohio Hopewell Archaeology, edited by P. Pacheco, pp. 36-52. The Ohio Archaeological Council, Inc, Columbus.

Thank you all for the interesting and useful references. Some I have read and some not yet! However, I did not make it clear enough in my question I'm afraid. I am not referring at all to the run-up to agriculture or domestication. Here in South Africa the Khoisan hunter-gatherers and herders never did embrace any form of agriculture or plant domestication. Both precolonial and post-colonial people used, and modern descendants still use, a wide variety of plants in all sorts of ways. So what I am asking is for evidence of use that has been found world-wide in excavation deposits, for use of plants, be they indigenous or, so-called weedy aliens, but with no connection to agriculture or domestication. Not only for food, but for medicinal, household, construction, toolmaking, dyeing, mastic, painting, and etc!