There are no weeds.
I hear you, dear Heaven (peace to you!), but I think some would disagree. Wikipedia has some really good thoughts about what constitutes a "weed." For example:
"... a plant in an undesired place."
"A plant that interferes with management objectives for a given area of land at a given point in time.
"Unwanted plants" because they... "are unsightly, or crowd out or restrict light to more desirable plants or use limited nutrients from the soil... can harbor and spread plant pathogens that infect and degrade the quality of crop or horticultural plants... a nuisance because they have thorns or prickles... have chemicals that cause skin irritation or are hazardous if eaten..."
The article does admit that "the term weed in its general sense is a subjective one, without any classification value, since a "weed" is not a weed when growing where it belongs or is wanted." And interesting definition by Professor Richard C. Lewontin of Harvard University is that weeds are "plants that create environmental conditions in which they themselves cannot reproduce..." and states that they "continue to exist, because the environment is continually being disturbed to create open conditions for new generations..."
Be all of that as it may, again I get your point, truly: all plants have some purpose/benefit. So, going forward, I will try not to use the term "weed." Because that is not the actual term used, anyway. The account actually refers to a specific plant, the "tares", which is "a kind of darnel, resembling wheat except the grains are black." The darnel spoken of in the account is thought to be Lolium temulentum (because of its abundance in the region) and, unfortunately, undesired by wheat farmers.. because it parasitizes wheat fields. As you can understand, while a darnel farmer might consider such a plant desirable... a wheat farmer would most assuredly consider it a "weed."
Again, peace to you!
A slave of Christ,
SA