Rutgers Gardens, New Brunswick - NJ, USA

The term weed is used in a variety of senses, generally centering around a plant that is not desired within a certain context. The term weed is a subjective one, without any classification value, since a plant that is a weed in one context is not a weed when growing where it belongs or is wanted. Indeed, a number of plants that many consider "weeds", are often intentionally grown by people in gardens or other cultivated-plant settings. Therefore, a weed is a plant that is considered by the user of the term to be a nuisance. The word commonly is applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More vaguely, "weed" is applied to any plants that grow and reproduce aggressively and invasively. The term weed has also been generalized to any species, not just plants, that can live in diverse environments and reproduce quickly, and the term has even been applied to humans.

Erigeron annuus (annual fleabane) is a plant in the daisy family, Asteraceae.

Erigeron annuus is a herbaceous plant with alternate, simple leaves, and green, sparsely haired stems. The flowers are white with yellow centers, borne in spring through fall.

Erigeron (pron.: /ɨˈrɪdʒərɒn/; syn. Stenactis Cass.) is a genus of about 390 species of daisy-like flowering plants in the family Asteraceae, sometimes confused with other closely related genera, Aster and the true daisy Bellis. The genus has a cosmopolitan distribution in dry, mountainous areas and grassland, with the highest diversity in North America, where 173 species occur.

Fleabane is a common name for some flowering plants in the family Asteraceae.

Most are in the subfamily Asteroideae:

One genus is in the related Cichorioideae

A wildflower (or wild flower) is a flower that grows in the wild, meaning it was not intentionally seeded or planted. Yet "wildflower" meadows of a few mixed species are sold in seed packets. The term "wildflower" has been made vague by commercial seedsmen who are interested in selling more flowers or seeds more expensively than when labeled with only its name and/or origin. The term implies that the plant probably is neither a hybrid nor a selected cultivar that is in any way different from the way it appears in the wild as a native plant, even if it is growing where it would not naturally.

"Wildflower" is not an exact term. Terms like native species (naturally occurring in the area, see flora), exotic or, better, introduced species (not naturally occurring in the area), of which some are labelled invasive species (that out-compete other plants – whether native or not), imported (introduced to an area whether deliberately or accidentally) and naturalized (introduced to an area, but now considered by the public as native) are much more accurate.

In the United Kingdom, the organisation Plantlife International instituted in 2002 the County Flowers scheme whereby members of the public nominated and voted for a wild flower emblem for their county. The aim was to spread awareness of the heritage of native species and about the need for conservation, as some of these species are endangered. For example, Somerset has adopted the Cheddar Pink (Dianthus gratianopolitanus), London the Rosebay Willowherb (Chamerion angustifolium) and Denbighshire/Sir Ddinbych in Wales the rare Limestone Woundwort (Stachys alpina).

The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies (derived characteristics). These characteristics include flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure; they are fruiting plants, although more commonly referred to as flowering plants.

The ancestors of flowering plants diverged from gymnosperms around 245–202 million years ago, and the first flowering plants known to exist are from 140 million years ago. They diversified enormously during the Lower Cretaceous and became widespread around 100 million years ago, but replaced conifers as the dominant trees only around 60–100 million years ago.

The Flora of North America North of Mexico (usually referred to as FNA) is a multivolume work describing the native plants of North America. Much of the Flora is already available online. It is expected to fill 30 volumes when completed, and will be the first work to treat all of the known flora north of Mexico.

It is a collaboration of over 800 authors, who collaborate over the web.