No one knows when weeds were discovered. It is likely that the humans came across weeds for the first time when they began cultivating land. Weeds would have been as much of a nuisance to them as they are to the farmers of less-developed nations today. The term ‘weed’ can be used to denote undesirable plants that grow aggressively. In the limiting sense, the word ‘weed’ refers to an unwanted plant in human-made settings such as agricultural areas, gardens and lawns.
Weeds are unwanted for a number of reasons. The main causes include:
(a) They crowd out more desirable plants and limit the sunlight reaching them, thus affecting their growth.
(b) Some weeds spread ‘pathogens’ (colloquially: harmful germs) and affect the quality of the crop being grown.
(c) Weeds with thorns make it difficult for a farmer to walk in his/her field without protection
(d) There are weeds which release chemicals that cause skin irritation.
(e) Most of the time, weeds are not edible and can cause sickness if eaten.
Weeds are generally better than the desired plants when it comes to survival techniques. This may explain why there are so many weeds found in the woods.