Introduction

There it is, a plant you don’t want in your field, lawn, garden, pond, or some other site where you have decided it shouldn’t grow. Why? What’s the matter with it? It is growing quite well, probably better than what you planted and want to grow there. However, you don’t want it because you regard it as a weed and the decision is yours. A weed is a plant growing where it is not desired (Buchholtz, 1967). The definition is clear. It is also clear, on examination, that the burden and responsibility for defining what plants are weeds rest with people who decide when a plant, in a particular place and time, is not desired. Human attitudes play a fundamental role in determining what plants are weeds. Weeds share the characteristic of being unwanted by some people.