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Plant Evolution And Classification, Evolution Of Plants, Classification Of Plants, Plant Structure, Plant Development

A plant is an organism in the kingdom Plantae. According to the five-kingdom classification system used by most biologists, plants have the following characteristics: they are multicellular during part of their life; they are eukaryotic, in that their cells have nuclei; they reproduce sexually; they have chloroplasts with chlorophyll-a, chlorophyll-b and carotenoids as photosynthetic pigments; they have cell walls with cellulose, a complex carbohydrate; they have life cycles with an alternation of a sporophyte phase and a gametophyte phase; they develop organs which become specialized for photosynthesis, reproduction, or mineral uptake; and most live on land during their life cycle.

Biologists have identified about 500,000 species of plants, although there are many undiscovered species in the tropics.

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