Plant
.
The
photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis radically changed the composition of the early Earth's atmosphere, which as a result is now 20% oxygen. Animals and most other organisms are aerobic, relying on oxygen; those that do not are confined to relatively rare anaerobic environments. Plants are the
primary producers in most terrestrial ecosystems and form the basis of the
food web in those ecosystems. Many animals rely on plants for shelter as well as oxygen and food.
Land plants are key components of the
water cycle and several other
biogeochemical cycles. Some plants have
coevolved with
nitrogen fixing bacteria, making plants an important part of the
nitrogen cycle. Plant roots play an essential role in
soil development and prevention of
soil erosion. The Earth's
biomes are named for the type of vegetation because plants are the dominant organisms in biomes.
Numerous animals have coevolved with plants. Many animals
pollinate flowers in exchange for food in the form of pollen or
nectar. Many animals
disperse seeds, often by eating
fruit and passing the seeds in their feces.
Myrmecophytes are plants that have coevolved with
ants. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from
herbivores and sometimes competing plants. Ant wastes provide organic
fertilizer.
The majority of plant species have various kinds of fungi associated with their root systems in a kind of
mutualistic symbiosis known as
mycorrhiza. The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for
endophytic fungi that protect the plant from herbivores by producing toxins. The fungal endophyte,
Neotyphodium coenophialum, in tall fescue (
Festuca arundinacea) does tremendous economic damage to the cattle industry in the U.S.
Various forms of parasitism are also fairly common among plants, from the semi-parasitic
mistletoe that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic
broomrape and
toothwort that acquire all their nutrients through connections to the roots of other plants, so have no chlorophyll. Some plants, known as
myco-heterotrophs, parasitize mycorrhizal fungi, and hence act as
epiparasites on other plants.
Many plants are
epiphytes, meaning they grow on other plants, usually trees, without parasitizing them. Epiphytes may indirectly harm their host plant by intercepting mineral nutrients and light that the host would otherwise receive. The weight of large numbers of epiphytes may break tree limbs. Many
orchids,
bromeliads,
ferns and
mosses often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata, complex aquatic food webs.
[Bromeliad Phytotelmata[1]]A few plants are
carnivorous, such as
Venus flytrap and
sundew. They trap small animals and digest them to obtain mineral nutrients, especially nitrogen.
Plant
fossils include roots, wood, leaves, seeds, fruit,
pollen,
spores,
phytoliths, and
amber (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments.
Pollen,
spores and algae (
dinoflagellates and
acritarchs) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide.
Early fossils of these ancient plants show the individual cells within the plant tissue. The Devonian period also saw the evolution of what many believe to be the first modern tree,
Archaeopteris. This fern-like tree combined a woody trunk with the fronds of a fern, but produced no seeds.
|
Fossil Ginkgo leaves from the Jurassic of England |
The
Coal Measures are a major source of
Palaeozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect;
coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Forest at Victoria Park in
Glasgow,
Scotland, the stumps of
Lepidodendron trees are found in their original growth positions.
The fossilized remains of conifer and angiosperm roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the
Mesozoic and
Caenozoic eras.
Sequoia and its allies,
magnolia,
oak, and
palms are often found.
Petrified wood is common in some parts of the world, and is most frequently found in arid or desert areas where it is more readily exposed by
erosion. Petrified wood is often heavily silicified (the organic material replaced by
silicon dioxide), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using
lapidary equipment. Fossil forests of petrified wood have been found in all continents.
Fossils of seed ferns such as
Glossopteris are widely distributed throughout several continents of the
southern hemisphere, a fact that gave support to
Alfred Wegener's early ideas regarding
Continental drift theory.
Nutrients from the soil are distributed to specific areas in the plant through vessels, for example to the leaves to conduct
photosynthesis. Also the
glucose produced during
photosynthesis is distributed around the plant to give the plant energy to keep growing and
seeding.
* Species estimate and counts:
**Prance, G. T. (2001). Discovering the Plant World.
Taxon 50: 345-359.
**International Union for Conservation of Nature and Natural Resources (IUCN) Species Survival Commission (2004). IUCN Red List of Threatened Species [
2].
**Both the above are cited in
Nature Conservancy, Spring 2006, p. 14.
* Kenrick, Paul & Crane, Peter R. (1997).
The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press. ISBN 1-56098-730-8.
* Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (2005).
Biology of Plants (7th ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1007-2.
* Taylor, Thomas N. & Taylor, Edith L. (1993).
The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-651589-4.
* Evans, L. T. (1998).
Feeding the Ten Billion - Plants and Population Growth. Cambridge University Press. Paperback, 247 pages. ISBN 0-521-64685-5.
* Trewavas, A. (2003).
Aspects of Plant Intelligence,
Annals of Botany 92: 1-20.
*
Biosphere*
Botany*
Flower*
Forest*
Fruit*
Garden*
Gardening*
Houseplant*
Photosynthesis*
Plant cell*
Plant defense against herbivory*
Prehistoric plants
*
Rapid plant movement*
Tree*
Vegetable*
Vegetation*
Tree of Life*
Interactive Cronquist classificationBotanical and vegetation databases
*
e-Floras (Flora of China, Flora of North America and others)*
United States of America*
Flora Europaea*
Australia*
Chilean plants at Chilebosque 
