Phaeophyta


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Related to Phaeophyta: Rhodophyta

Phaeophyta

(fēŏf`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 those organisms commonly called brown algae. Many of the world's familiar seaweedsseaweed,
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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 are members of Phaeophyta. There are approximately 1,500 species. Like the chrysophytes (see ChrysophytaChrysophyta
, phylum (division) of unicellular marine or freshwater organisms of the kingdom Protista consisting of the diatoms (class Bacillariophyceae), the golden, or golden-brown, algae (class Chrysophyceae), and the yellow-green algae (class Xanthophyceae).
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), brown algae derive their color from the presence, in the cell chloroplasts, of several brownish carotenoid pigments, including fucoxanthin, in addition to the photosynthetic pigments chlorophyll a and c. With only a few exceptions, brown algae are marine, growing in the colder oceans of the world, many in the tidal zone, where they are subjected to great stress from wave action; others grow in deep water. Among the brown algae are the largest of all algae, the giant kelps, which may reach a length of over 100 ft (30 m). Fucus (rockweed), Sargassum (gulfweed), and the simple filamentous Ectocarpus are other examples of brown algae.

The cell wall of the brown algae consists of a cellulose differing chemically from that of plants. The outside is covered with a series of gelatinous pectic compounds, generically called algin; this substance, for which the large brown algae, or kelps, of the Pacific coast are harvested commercially, is used industrially as a stabilizer in emulsions and for other purposes. The normal food reserve of the brown algal cell is a soluble polysaccharide called laminarin; mannitol and oil also occur as storage products. The body, or thallus, of the larger brown algae may contain tissues differentiated for different functions, with stemlike, rootlike, and leaflike organs, the most complex structures of all algae.

Some groups of brown algae have evolved an interesting type of alternation of generations, in which physiologically independent haploid gametophyte plants produce gametes, the fusion of which initiates the diploid sporophyte generation. The mature sporophyte plant produces, through meiosismeiosis
, process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells (ovum and sperm), are being formed.
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, haploid spores, which develop into new gametophytes. The two generations, or phases, may be indistinguishable in size and form, or they may differ greatly. The genus Ectocarpus, for example, is found growing attached to larger algae. It has similar-looking gametophyte and sporophyte plants. In the kelps, however, the gametophyte is only a microscopic filament, in contrast to the occasionally tree-sized sporophyte.

Bibliography

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).

Phaeophyta

[fē′äf·əd·ə]
(botany)
The brown algae, constituting a division of plants; the plant body is multicellular, varying from a simple filamentous form to a complex, sometimes branched body having a basal attachment.
References in periodicals archive ?
In Phaeophyta, 0.5% and 2.5% Pachydictyon coriaceum methanol extract and 2.5% Colpomenia bullosa extract were also extremely larvicidal, as was a methanol extract of Rhodophyta species Gelidium amansii at 2.5%.
In the present study, brown algae (Phaeophyta) and pocilloporid coral recruits were dominant in reefs affected by terrestrial run-off explaining the high recruit numbers but low diversity in these reefs.
Many of the world's familiar seaweeds are members of Phaeophyta. Like the chrysophytes brown algae derive their color from the presence, in the cell chloroplasts, of several brownish carotenoid pigments, as fucoxathin.
Table 1: Examples of Marine Macroalgae PHYLUM GENUS COMMON NAME EXAMPLE Phaeophyta: Alaria Kelp, bladderlocks Alaria esculenta Ascophyllum Egg wrack Ascophyllum nodosum Ecklonia Kelp Ecklonia maxima Phaeophyta: Laminaria sp.
Demographic studies of the annual kelps Nereocystis luetkeana and Costaria costata (Laminariales, Phaeophyta) in Puget Sound, Washington.
Distribution of brown seaweeds (Phaeophyta) in the Yucatan Peninsula, Mexico.
(Laminariales: Phaeophyta) in the Alaskan Beaufort Sea.
Toxicity tests using developmental stages of Hormosira banksii (Phaeophyta) identify ammonium as a damaging component of secondary treated sewage effluent discharged into Bass Strait, Victoria, Australia.
Seaweeds are classified in terms of their pigments, nutrient contents and chemical composition as Rhodophyta, Phaeophyta or Chlorophyta whereas seagrasses have no real taxonomical classification.
The study on antiproliferative activity of crude extracts of ten Phaeophyta species isolated from Brittany coasts against three human cancers, human leukaemic T cell lymphoblast (Jurkat), human Burkitt's lymphoma (Daudi), and human chronic myelogenous leukaemia (K562) cells, showed strong antitumor potential of Sargassaceae species, Dictyota dichotoma, and Desmarestia ligulata [15].