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(klōrŏf`ətə), phylum (division) of the kingdom ProtistaProtista
or Protoctista
, in the five-kingdom system of classification, a kingdom comprising a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms.
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 consisting of the photosynthetic organisms commonly known as green algaealgae
[plural of Lat. alga=seaweed], a large and diverse group of primarily aquatic plantlike organisms. These organisms were previously classified as a primitive subkingdom of the plant kingdom, the thallophytes (plants that lack true roots, stems, leaves, and flowers).
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. The organisms are largely aquatic or marine. The various species can be unicellular, multicellular, coenocytic (having more than one nucleus in a cell), or colonial. Those that are motile have two apical or subapical flagella. A few types are terrestrial, occurring on moist soil, on the trunks of trees, on moist rocks, and even in snowbanks. Various species are highly specialized, some living exclusively on turtles, sloths, or within the gill mantles of marine mollusks.

It is generally accepted that early chlorophytes gave rise to the plants. Cells of the Chlorophyta contain organelles called chloroplastschloroplast
, a complex, discrete green structure, or organelle, contained in the cytoplasm of plant cells. Chloroplasts are reponsible for the green color of almost all plants and are lacking only in plants that do not make their own food, such as fungi and nongreen parasitic
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 in which photosynthesis occurs; the photosynthetic pigments chlorophyll a and chlorophyll b, and various carotenoids, are the same as those found in plants and are found in similar proportions. Chlorophytes store their food in the form of starch in plastids and, in many, the cell walls consist of cellulose. Unlike in plants, there is no differentiation into specialized tissues among members of the division, even though the body, or thallus, may consist of several different kinds of cells. There are four evolutionary lineages of green algae. Most living species are grouped in classes that are coextensive with three of these lineages.

Class Chlorophyceae

This group contains the largest number of species of the division. They can have two or more flagella, near the apex of the cell. Mitosis in this class involves phycoplasts, microtubules that develop between and separate the daughter nuclei. This characteristic is not seen in any other organism, implying that no organisms have descended from this class. There are a variety of asexual and sexual reproductive techniques. Sexual reproduction is characterized by the formation of a zygospore (a dormant diploid zygote protected by a thick wall) that later undergoes meiosis.

The class includes unicellular organisms such as those in the genus Chlamydomonas with their two apical flagella and nonmotile organisms such as Chlorella, which is being cultivated for use as a dietary supplement. Colonial genera of Chlorophyceae include Hydrodictyon (the "water net") and the so-called volvocine line of flagellated specimens that range from simple colonies of Gonium to the intricate spinning spheres of Volvox, which can consist of up to 60,000 cells and exhibit some cellular specialization. The most complex of the class are the filamentous members, some of which exhibit features that are seen primarily in plants. Despite this similarity the class is not believed to have been the evolutionary source of plants.

Class Charophyceae

Charophyceae are of great fossil age; the stoneworts date as far back as the late Silurian period. Cells of this class are asymetrical. Those that are motile have two flagella, at right angles near the apex of the cell. Sexual reproduction in this class, as in Chlorophyceae, is characterized by the formation of a zygospore and zygotic meiosis. Unlike in the other two common classes of green algae, but as with plants, the nuclear envelope disintegrates when mitosis begins. During cell division the mitotic spindle is present; in some a phragmoplast similar to those seen in plants aids in the formation of a cell plate. Plants are thought to have evolved from early species of Charophyceae.

The class includes Spirogyra, familiar filamentous algae that float on ponds and lakes in slimy masses. The desmids are single cells noted for their extraordinary symmetry and geometrical beauty. They are found only in fresh (usually still) water and often take an important place in the food chains of small nutrient-poor ponds and peat bogs. The stoneworts consist of a complex branched thallus with an erect stemlike structure and many whorls of short branches. They occur in shallow fresh or brackish water and especially in water rich in calcium, where they become stiff and lime-encrusted, a characteristic that has made them plentiful in the fossil record.

Class Ulvophyceae

Ulvophyceae contains marine organisms that take a variety of shapes that may consist of a few cells, long filaments, thin sheets of cells, or coenocytic cells. Most approach being radially symmetrical. They have an alternation of generations and unlike in the other classes, meiosis occurs in the spores rather than the zygotes. When present, there can be two or more apical flagella. During mitosis, the nuclear envelope and the mitotic spindle persist, as they do in the Charophyceae.

The class Ulvophyceae includes sea lettuce, or Ulva, bright green, leaflike algae that grows in shallow waters on rocks and piers. Ventricaria is an egg-shaped, coenocytic alga, familiar in warm seas. Some organisms of Ulvophyceae produce toxins that discourage predation. The chloroplasts of some others become symbionts after they are retained in the bodies of sea slugs that eat the algae. They continue to perform photosynthesis, providing the slug with needed oxygen.

See also seaweedseaweed,
name commonly used for the multicellular marine algae. Simpler forms, consisting of one cell (e.g., the diatom) or of a few cells, are not generally called seaweeds; these tiny plants help to make up plankton.
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See H. C. Bold and M. J. Wynne, Introduction to the Algae: Structure and Reproduction (1985); C. A. Lembi and J. R. Waaland, Algae and Human Affairs (1988); C. van den Hoek, Algae: an Introduction to Phycology (1994).

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The green algae, a highly diversified plant division characterized by chloroplasts, having chlorophyll a and b as the predominating pigments.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In 2005-2015, some phytoplankton components (CY and chlorophytes) and total FBM displayed an inverse correlation with the WL in summer, both in the pelagial (r = -0.16, p < 0.006) and in the littoral (r = -0.24, p = 0.016).
Pigment Abbreviation Occurrence Zeaxanthin ZEA Cvanobacteria Divinyl Chlorophyll a DIVa Prochlorophytes Fucoxanthin FUC Diatoms Peridinin PER Dinoflagellates 19'-Butanoyloxyfucoxan- BUT Chrysophytes 19'-Hexanoyloxyfucoxan- HEX Prymnesio- Chlorophyll b CHLb Chlorophytes Pigment Major groups Zeaxanthin Divinyl Chlorophyll a Prokaryotic picoplankton Fucoxanthin Large cukaryotes Peridinin 19'-Butanoyloxyfucoxan- 19'-Hexanoyloxyfucoxan- Eukaryotic nanoflagellates Chlorophyll b Table 2.
Diatoms and chlorophytes were dominant members of the periphyton throughout the study period.
Of the many phytoplankton taxa identified, this paper presents the results only for chlorophytes in general, Anabaena sp., and Microcystis sp.
Among the small algae (d < 40 gm) chlorophytes prevailed followed by cryptophytes and discoid diatoms (genera Cyclotella, Stephanodiscus, Cyclostephanos) and chrysophytes + haptophytes.
chlorophytes, indicating that their respective chl b synthesis genes may
Using additional diagnostic chlorophyll and carotenoid photopigments as indicators of major phytoplankton functional groups (i.e., diatoms, dinoflagellates, chlorophytes, cyanobacteria, cryptomonads), we can examine the interactive effects of nutrient and hydrologically driven changes of phytoplankton community composition and activity.
Flexuous seaweeds, such as chlorophytes of the genus Boodlea, phaeophytes of the genus Dictyota, and rhodophytes of the genera Galaxaura and Padina, form scattered populations.
As in the previous experiment, cyanobacteria and chlorophytes were significantly enhanced by gizzard shad (Fig.
The colonial chlorophyte Eudorina and the filamentous green alga Oedogonium were the dominant taxa in mixed-species treatments, whereas the filamentous green algae Cladophora and Mougeotia were dominant in grazer-free controls (Table 3).
Domination of diatoms in spring and the increased proportion of small flagellates with a large variety of chlorophytes in summer are typical of streams and rivers of the temperate climate region (Reynolds et al., 1994; Tipping et al., 1997).
Juveniles didn't grow as well when fed with chlorophytes, that was justified by the lack of a substantial amount of polyunsaturated fatty acids (PUFA) and by their low nutritional value (Pohl and Zurheide, 1979; Paterson, 1984; Ahlgren et al., 1992; Beck, 2001; Beck and Neves, 2003).