A botanist can't examine a plant and tell if it is a weed. A chemist can examine a liquid and determine if it is water.
This is because, despite being a common language term, "water" maps to a specific chemical compound.
"Weed" is a common language term that maps to nothing in a scientific context. RoundUp is an herbacide, it only becomes slective, i.e. "a weedkiller" when some plants are genetically modified and this because we define "weeds" as whatever plants Roundup kills.
The set of weeds for a horticulturist is different from the set of weeds for an agronomist and both are different from the set of weeds for an ecologist - and more importantly, the horticulturist's weeds and the ecologist's weeds will tend toward polar opposites.
The same is of course true with the agronomist. Thus a natural food bearing plant is described as a weed in the article.
The premises upon which the article are based are economic not scientific despite the name of the publication.
Unless the meaning of "water" has changed sometime in the past second, water is the liquid form of the chemical substance dihydogen oxide (i.e., H2O). This is the same meaning its had since the atomic components of water were first determined...
