Brief SummaryRead full entry
IntroductionThe 250,000-380,000 currently-known plant species (2,7,8,11) , or members of the kingdom Plantae, are organisms that live on every continent and in nearly every habitat on Earth (10). Plants include some of the primarily water-dwelling organisms called green algae (specifically a group known as the charophyte algae(12)), and the embryophytes or land plants which evolved from green algae (1,12,14). A sometimes-used broader definition of plants also includes the rest of the green algae as well as red algae and glaucophyte algae (9,14). The subset of plants called land plants is divided into two main groups itself: nonvascular plants (those that lack specialized systems allowing them to transport water and nutrients internally; these include mosses, hornworts, and liverworts (5,7)); and vascular plants (those that do have vascular transport systems; these include ferns, lycophytes, gymnosperms, and the highly diverse flowering plants (14)). Plants have special cell walls around each of their cells built in large part out of a carbohydrate called cellulose (7) that makes them especially strong and firm (6). Unlike most other organisms, most plants produce their own food through a process called photosynthesis (9), in which they soak up sunlight, usually with their leaves, and deploy this sunlight within a complicated biochemical system to turn carbon dioxide combined with water into energy-rich sugars (3,15). Through this process, plants have a crucial effect on the global climate and the environment—they remove carbon dioxide, a gas that contributes to global warming, from the air (13), and release oxygen, which is essential for animals, fungi, protists, many bacteria, and even plants themselves in order for them to extract energy from organic molecules (4,15). In addition, plants provide food and shelter for many kinds of organisms, and humans rely on them directly for grains, vegetables, fruits, wood, paper, clothing, and many medicines (8,11). In the future, they may be useful as sources for new medical drugs (8), emerging cleaner, renewable fuels, and other products (6). For all of these reasons and more, plant conservation is critically important (2,8,11).