Green plants have cell walls with cellulose and characteristically obtain most of theirenergy from sunlight via photosynthesis using chlorophyll contained in chloroplasts, which gives them their green color. Some plants are parasitic and may not produce normal amounts of chlorophyll orphotosynthesize. Plants are also characterized by sexual reproduction, modular and indeterminate growth, and an alteration of generations, although asexual reproduction is common, and some plants bloomonly once while others bear only one bloom.
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, some260–290 thousand, are seed plants (see the table below). Green plants provide most of the world's free oxygen and are the basis of most of the earth's ecologies, especially on land. Plants described asgrains, fruits and vegetables form mankind's basic foodstuffs, and have been domesticated for millennia. Plants enrich our lives as flowers and ornaments. Until recently and in great variety they haveserved as the source of most of our medicines and drugs. Their scientific study is known as botany.
1.1 Current definitions of Plantae
3 Structure, growth, and development
3.1 Factors affecting growth
3.2 Plant cell
4.2 Immune system
5.2 Ecological relationships
6.2 Nonfood products
6.3 Aesthetic uses
6.4 Scientific and cultural uses
6.5 Negative effects...