They will discover at the roadside the most humble, obscure, and unwanted plant, dig it up, carry it home, and build their wildflower garden around it. But unless they can convince others, lots of others, that they have done something wise and worth copying, their statement is lost on society. The act of being valued by a single person is not usually enough to make a sow's ear weed into a silk purse flower. Lawrence J. King codifies such an approach in his Weeds of the World . He tries to come up with a list of objective characteristics that apply to plants that we regard as weeds.
Weeds are spontaneous , appearing without being sown or cultivated.
Weeds have a high reproductive capacity , producing large numbers of seeds or having a rank vegetative reproduction. I can think of weeds that are sterling examples of these characteristics. My own garden is currently purslane-free, but my neighbor's garden is a purslane battlefield. Purslane is an annual, but it sets seeds so persistently that, unlike other annuals, it can't readily be cultivated away. I don't think I have ever seen a weed produce so much vegetable mass in so short a time.