The word weed has become increasingly associated with marijuana, the plant that’s used recreationally and medicinally. But the word “weed” actually has a long history, with different meanings at different times.
In some contexts, it refers to plants considered undesirable in a particular situation, growing where they conflict with human preferences, needs or goals. In agriculture, for example, a field of weeds would compete with cultivated crops for sunlight, soil moisture and nutrients. In the wild, invasive exotic species can overtake native vegetation and disrupt ecosystems over large geographic areas.
Weeds are often referred to as nuisance plants, although some of them have value. In the case of dandelion and clover, for instance, their flowers attract pollinators that are important for the health of bees, birds and other organisms that depend on plants for food. Some of the most noxious weeds, like wild mint or poppy, can be used to make pharmaceuticals, including the antidepressant THC and the seizure medication Epidiolex, which was recently approved by the FDA for two rare types of epilepsy.
The best way to identify weeds is by looking at the entire plant, and then by comparing it to a weed ID manual or other guide. A good manual typically provides a series of “either-or” pairs of characteristics that allow you to narrow down the possible identifications until you arrive at a single or small list of options for the specimen in question. You can also try using an app like Google Lens, which uses your smartphone’s camera to identify objects and plants.