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Sunday, March 20, 2011

Plants (1)

Plants
Temporal range:
Early Cambrian to recent, but see text, 520–0 Ma

Scientific classification
Domain: Eukaryota
(unranked): Archaeplastida
Kingdom: Plantae
Haeckel, 1866[1]
Divisions
Green algae
Land plants (embryophytes)
Nematophytes
Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, flowers, 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.

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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.

Current definitions of Plantae

When the name Plantae or plant is applied to a specific taxon, it is usually referring to one of three concepts. From least to most inclusive, these three groupings are:
Name(s) Scope Description
Land plants, also known as Embryophyta or Metaphyta. Plantae sensu strictissimo This group includes the liverworts, hornworts, mosses, and vascular plants, as well as fossil plants similar to these surviving groups.
Green plants - also known as Viridiplantae, Viridiphyta or Chlorobionta Plantae sensu stricto Includes the land plants plus Charophyta (i.e. stoneworts), and Chlorophyta (i.e., other green algae such as sea lettuce). Viridiplantae encompass a group of organisms that possess chlorophyll a and b, have plastids that are bound by only two membranes, are capable of storing starch, and have cellulose in their cell walls. It is this clade which is mainly the subject of this article.
Archaeplastida, Plastida or Primoplantae Plantae sensu lato Comprises the green plants above plus Rhodophyta (red algae) and Glaucophyta (glaucophyte algae). This clade includes the organisms that eons ago acquired their chloroplasts directly by engulfing cyanobacteria.
Outside of formal scientific contexts, the term "plant" implies an association with certain traits, such as multicellularity, cellulose, and photosynthesis.[2][3] Many of the classification controversies involve organisms that are rarely encountered and are of minimal apparent economic significance, but are crucial in developing an understanding of the evolution of modern flora.

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