A weed is a plant which is generally considered to be a nuisance and is mostly looked upon with disgust. Even a Shakespearean sonnet has to say as much for this plant, "Cursed is the ground because of you; through painful toil you will eat of it all the days of your life. It will produce thorns and thistles for you and you will eat the plants of the field. By the sweat of your brow you will eat your food until you return to the ground."
The term weeds are generally used in context of the unnecessary plants that grow in our lawns, gardens and agricultural fields which do not have any productive value. In more specific terms, weeds refer to that category of plants which grow and reproduce aggressively. According to J M Torell in the Weeds of the West, weed is "A plant that interferes with management objectives for a given area of land at a given point in time." Generally speaking a weed is a plant in an undesired place.
One of the important features of the weed seeds is that they germinate early, seedlings grow faster and they also flower early. This leads to a profusion of seeds way ahead of the crop they infest. And so these seeds are unwarily transported to different places along with the crop produce and get distributed along the way. Weeds have an unusual quality of surviving in the most adverse conditions.
Weeds also have an intrinsic capacity to germinate under varied conditions even though they are season-bound and germination takes place in certain seasons in regular succession. Yet they can preserve their viability for years even under adverse conditions. They can take shape even after being dormant for a longer period.
Weeds belong to the Angiosperm (flowering plants) category which has two further sub-classes: Monocots and Dicots. They can be further classified on the basis of their habitat; namely terrestrial and aquatic categories respectively. On the basis of the duration of their life, weeds are categorized as Annuals, Biennials and Perennials.
The Annual type of weeds lives and produce their seeds in a single growing season. The Biennials need two growing seasons to live and flourish. Both these class of weeds grow through seeds. But the Perennials live indefinitely and are propagated through vegetations too.
Some of the better known perennials take their origins in the rhizomes, stolons, bulbs and tubers. There are two types of perennials weeds, namely the simple one and a creeping variety. The simple ones multiply and grow through seeds. On the other hand, the creeping perennial weeds are spread by creeping roots or the above ground stems and at times by the underground stems or rhizomes.
There are many opposing thoughts as to the usefulness or the nuisance value of the weeds. Some of the experts are more lenient towards these plants and it is amply clear in the last stanza of Gerard Manley Hopkins' poem Inversnaid when he says" What would the world be, once bereft of wet and wildness? Let them be left, O let them be left, wildness and wet; Long live the weeds and the wilderness yet."
Doug Larson has an indulgent outlook towards weeds when he says "A weed is a plant that has mastered every survival skill except for learning how to grow in rows."
Thus, the whole attitude towards looking at these plants entirely depends and varies from person to person. Weeds can be both a boon and a bane depending on their location and the place where they grow.