I think this is a very difficult subject as all plants are weeds. A definition of what is a weed is very necessary but extremely difficult in reality. The one that says a weed is a plant out of place is really the only realistic one without getting very technical. Some use the term where a plant has a commercial consequence and causes loss of production in some area or for example contaminates wool from sheep. I am not sure that there is any plant that is not a weed. Is there a universal definition that could be adopted? I have my doubts. Regards Don Journet South Eastern Australia