Brown Algae

brown algae: see Phaeophyta.

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brown algae [¦brau̇n ¦al·jē]

(botany)

The common name for members of the Phaeophyta.

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Brown Algae 

(Phaeophyta), a type of sporiferous plants, including 240 genera (1,500 species), of which three are freshwater, the rest marine. The thallus is olive green to dark brown because of the presence in the chromatophores of the special brown pigment, fucoxanthin (C₄₀H₅₆O₆), which masks other pigments (chlorophyll a, chlorophyll c, xanthophyll, and beta-carotene).

Brown algae are varied in form and size, ranging from microscopic, branched threads to 40-meter plants. In higher brown algae (for example, Laminariaceae) differentiation of tissues and the development of conducting elements are observed. Multicellular fibers with a basal growth zone, absent in other algae, are characteristic of brown algae. The cell walls contain cellulose and specific substances—algin and fucoidin. There is usually one nucleus in each cell. The chromatophores are small and disclike. In some species of brown algae there are pyrenoids, which bear little resemblance to those of other algae. Colorless vesicles of fucosan, which has many properties of tannin, accumulate around the nucleus of the cell. Stored in the tissues of brown algae as reserves are mannitol (a polyatomic alcohol), laminarin (a polysaccharide), and more rarely, oil.

Brown algae reproduce sexually and asexually, rarely vegetatively. They usually have a sporophyte and a gametophyte, which alternate strictly in higher families (Laminariaceae and Desmarestiaceae). In Cyclosporeae the gametophytes develop on the sporophytes; in primitive brown algae (Ectocarpaceae, Chordaceae, Cutleriaceae, and others) the gametophyte or sporophyte may fall outside the cycle of development or appear once in several generations. The reproductive organs are unilocular or multilocular sporangia. The multilocular sporangium, which most often functions as a gametangium, is formed as one cell or a series of cells divided by septa into chambers, each containing one gamete or spore. Meiosis usually occurs in unilocular sporangia; in Dictyotaceae, it occurs in tetrasporangia. The sexual process is isogamous, heterogamous, or oogamous. The pear-shaped spores and gametes, usually with one eyelet, have two flagella on the side, one directed forward and one backward.

Brown algae are divided into three classes: Aplanosporophyceae (only Dictyotaceae), Phaeosporophyceae (heterogeneratae and isogeneratae, except for Dictyotaceae), and Cyclosporophyceae (Cyclosporeae). Brown algae are distributed in all seas, especially cold ones, where they form large growths. They are a source of alginic acids and their salts—alginates—as well as of fodder meal and a powder used in medicine which contains iodine and other microelements. Some brown algae are used as food.

REFERENCES

Kursanov, L. I. Burye i krasnye vodorosli. Moscow, 1927.
Zinova, E. S. Vodorosli laponskogo moria (burye). Vladivostok, 1929. (lzv. Tikhookeanskoi nauchno-promyslovoi stantsii, vol. 3, issue 4.)
Zinova, A. D. Opredelitel’ burykh vodoroslei severnykh morei SSSR. Moscow-Leningrad, 1953.

IU. E. PETROV