A weed is any plant that grows in a situation where it is unwanted. This applies to plants of the field and to cultivated types. Most are generalists and grow in any soil, and are sometimes invasive. They compete with cultivated plants for nutrients, light and moisture. They are unsightly, and are important hosts to pests and diseases. There are four main types:

Annuals: Which grow from seed, flower, set seed and die in a year. They produce large amounts of seed.

Herbaceous perennials: Have storage roots underground. The shoots emerge each spring and die down in winter. They usually propagate by creeping stems.

Woody Perennials: Leaves emerge from thick stems which survive the winter above ground.

Evergreens: Maintain foliage all year round, and grow and shed leaves continuously.

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