In nature, plants, also called green plants (Viridiplantae in Latin), are living multicellular organisms of the kingdom Plantae. They form a clade that includes:
- the flowering plants,
- conifers and other gymnosperms,
- liverworts and
- as well as, depending on definition, the green algae.
Plants exclude the red and brown algae, and some seaweeds such as kelp, the fungi, archaea and bacteria.
Green plants have cell walls with cellulose and characteristically obtain most of their energy from sunlight via photosynthesis using chlorophyll contained in chloroplasts, which gives them their green colour.
Some plants are parasitic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are also characterized by sexual reproduction, modular and indeterminate growth, and an alternation of generations, although asexual reproduction is common.
Numbers of species of plants
Precise numbers are difficult to determine, but as of 2010, there are thought to be 300–315 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants (see the table below).
Green plants provide most of the world's molecular oxygen[ though blue green algae also provide a lot too] and are the basis of most of the earth's ecologies, especially on land.
Plants described as grains, fruits and vegetables form mankind's basic foodstuffs, and have been domesticated for millennia. Plants serve as ornaments and, until recently and in great variety, they have served as the source of most medicines and drugs. Their scientific study is known as botany, a branch of biology.
Source adapted from: http://en.wikipedia.org/wiki/Plant