Plant are
Living Organisms belonging to the
Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of
Plants, defined as seed
Plants, bryophytes, ferns and fern allies. As of 2004, some 287,655 species had been identified, of which 258,650 are flowering and 18,000 bryophytes (see table below).
Green plants, sometimes called
Viridiplantae, obtain most of their energy from sunlight via a process called photosynthesis.
Definition
Aristotle divided all living things between
Plants (which generally do not move), and animals (which often are mobile to catch their food). In Linnaeus' system, these became the
Kingdoms Vegetabilia (later Metaphyta or Plantae) and Animalia (also called Metazoa). Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new
Kingdoms. However, these are still often considered
Plants in many contexts, both technical and popular.
Diversity
About 350,000 species of
Plants, defined as seed
Plants, bryophytes, ferns and fern allies, are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are
Flowering plant, 16,000 bryophytes, 11,000 ferns and 8,000 green algae.
Phylogeny
A proposed phylogenetic tree of Plantae, after Kenrick and Crane, is as follows, with modification to the Pteridophyta from Smith et al. The Prasinophyceae may be a paraphyletic basal group to all
Green plants.
Structure, growth, and development
Most of the solid material in a plant is taken from the atmosphere. Through a process known as photosynthesis, most
Plants use the energy in sunlight to convert carbon dioxide from the atmosphere, plus water, into simple sugars. Parasitic
Plants, on the other hand, use the resources of its host to grow. These sugars are then used as building blocks and form the main structural component of the plant. Chlorophyll, a green-colored, magnesium-containing pigment is essential to this process; it is generally present in plant leaves, and often in other plant parts as well.
Plants usually rely on soil primarily for support and water (in quantitative terms), but also obtain compounds of nitrogen, phosphorus, and other crucial elemental nutrients. Epiphytic and lithophytic
Plants often depend on rainwater or other sources for nutrients and carnivorous
Plants supplement their nutrient requirements with insect prey that they capture. For the majority of
Plants to grow successfully they also require oxygen in the atmosphere and around their roots for respiration. However, some
Plants grow as submerged aquatics, using oxygen dissolved in the surrounding water, and a few specialized vascular
Plants, such as mangroves, can grow with their roots in anoxic conditions.
Factors affecting growth
The genotype of a plant affects its growth. For example, selected varieties of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.
Growth is also determined by environmental factors, such as temperature, available water, available light, and available nutrients in the soil. Any change in the availability of these external conditions will be reflected in the
Plants growth.
Biotic factors are also capable of affecting plant growth.
Plants compete with other
Plants for space, water, light and nutrients.
Plants can be so crowded that no single individual produces normal growth, causing etiolation and chlorosis. Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of mycorrhizal fungi, and attacks by insects or plant diseases, including those caused by bacteria, fungi, viruses, and nematodes.
Simple
Plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Other
Plants may be organized according to their seasonal growth pattern: annual
Plants live and reproduce within one growing season, biennial
Plants live for two growing seasons and usually reproduce in second year, and perennial
Plants live for many growing seasons and continue to reproduce once they are mature. These designations often depend on climate and other environmental factors;
Plants that are annual in alpine or temperate regions can be biennial or perennial in warmer climates. Among the vascular
Plants, perennials include both evergreens that keep their leaves the entire year, and deciduous
Plants which lose their leaves for some part of it. In temperate and boreal climates, they generally lose their leaves during the winter; many tropical
Plants lose their leaves during the dry season.
The growth rate of
Plants is extremely variable. Some mosses grow less than 0.001 millimeters per hour (mm/h), while most trees grow 0.025-0.250 mm/h. Some climbing species, such as kudzu, which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h.
Immune system
By means of cells that behave like nerves,
Plants receive and distribute within their systems information about incident light intensity and quality. Incident light which stimulates a chemical reaction in one leaf, will cause a chain reaction of signals to the entire plant via a type of cell termed a "bundle sheath cell". Researchers from the Warsaw University of Life Sciences in Poland, found that
Plants have a specific memory for varying light conditions which prepares their immune systems against seasonal pathogens.
Internal distribution
Vascular
Plants differ from other
Plants in that they transport nutrients between different parts through specialized structures, called xylem and phloem. They also have roots for taking up water and minerals. The xylem moves water and minerals from the root to the rest of the plant, and the phloem provides the roots with sugars and other nutrient produced by the leaves.
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