Division Chlorophyta (Green Algae)
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A quiet pond on Palomar Mountain (San Diego County, California) covered with dense masses of the filamentous green alga Spirogyra. This interesting alga also goes by the uncomplimentary vernacular name of "pond scum."
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Sea lettuce (Ulva californica and possibly also U. lactuca), a common green alga that grows on the intertidal rocks of San Diego County, California. In some countries this alga is eaten in soups.
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Wawaeiole (Codium), another intertidal green alga that is sold in Hawaiian markets. Like the green alga Ulva, it is cooked and eaten in soups. The rubbery thallus of this genus is coenocytic, composed of numerous microscopic, multinucleate filaments. According to E. Yale Dawson (Marine Botany, 1966), the Hawaiians developed the most diversified dietary use of seaweeds with 75 species used regularly as food.
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Water net (Hydrodictyon reticulatum), an interesting fresh-water green alga with cells arranged in pentagons and hexagons. It is occasionally found in ponds throughout San Diego County, California. This unique alga is able to reproduce very rapidly because each cell of the net in turn produces a new cylindrical net of small cells within it. Upon escape from the parent cell, the miniature net enlarges enormously and each of its cells produces another miniature net.
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Trentepohlia aurea, a striking green alga that grows on the trunks of Monterey cypress (Cupressus macrocarpa) in coastal central California. The bright orange coloration is due to carotenoid pigments in the cells of this alga.
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Division Charophyta (Stoneworts)
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A pond containing the freshwater alga Chara in the Coast Ranges of northern California. This division is called "stoneworts" because the branched thallus is often encrusted with lime (calcium and magnesium carbonates). Because of their calcareous encrustation, members of the division Charophyta are often preserved in the fossil record. Paleotologists can readily recognize exinct relatives of Chara from strata as early as the Devonian Period, over 300 million years ago.
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Close-up view of the fruiting branches of Chara showing the easily recognizable sex organs. Although microscopic, the sex organs can be readily identified by their shape and color. The sperm-bearing antheridia are bright orange, while the egg-bearing oogonium is green with a distinctive crown of cells. This is an excellent alga for studying life cycles in general biology and botany classes. What is especially remarkable about this photo is that it was NOT taken with a microscope. It was taken with a hand-held digital camera (Sony T-1).
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Division Phaeophyta (Brown Algae)
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Elk kelp (Pelagophycus porra), a large brown alga that grows off the coast of San Diego County, California. The large, buoyant air bladder at the tip of a thick stipe supports this large kelp in the water. Two main branches have photosynthetic blades that hang down in the water like giant curtains.
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Upper Photo: Beds of giant bladder kelp (Macrocystis pyrifera) off the coast of southern California. Lower photo: Giant bladder kelp washed ashore on a sandy beach showing the large, root-like holdfast and blades with basal air bladders. This species is harvested by a moter driven barge called a kelp cutter, up to 300 tons in a single load. Each year, thousands of tons of wet kelp are processed into the valuable thickening agent called algin. The harvesting of this ecologically important seaweed is carefully regulated by the California State Department of Fish and Game.
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A submarine forest of giant bladder kelp (Macrocystis pyrifera) and feather boa (Egregia menziesii) along the coast of central California ( San Simeon, San Luis Obispo County).
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Dried kelp (Laminaria sp.) sold in Asian markets for food.
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Division Chrysophyta (Diatoms)
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Assorted diatoms. The ornamented valves surrounding each cell are impregnated with silica. Diatoms are a vital primary link in ocean food webs and are a major producer of oxygen through photosynthesis. Photographed through an Olympus compund microscope with Sony V-3 camera. Magnification 400x.
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Rectangular diatoms stacked together. The ornamentation along the edges of cells gives them the appearance of minute rulers. Collected at the surface of a desiccated small drainage on the Santa Rosa Plateau of Riverside County, California.
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Division Rhodophyta (Red Algae)
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The red alga Gelidium pulchrum from the intertidal zone of San Diego County, California. Gelidium is one of the red alga species harvested for the polysaccharide gum called agar (agar-agar). A larger species (Gelidium cartilagineum) from deeper waters was extensively harvested by divers along the southern California coast during World War II when Japanese agar supplies were cut off. Gelidium for agar manufacture is now collected extensively in Baja California.
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Powdered agar called agar-agar is commonly sold in Asian food stores. The name "agar-agar" is of Malay origin and means "jelly." Agar-agar is used as a thickening agent in foods much like gelatin is used. Most agars come from the Rhodopyta, including the genera Gelidium, Pterocladia and Gracilaria. Gelatin is a thickening agent or hydrogel derived from collagen protein in fibrous animal connective tissue and is the key ingredient in JELLO® desserts.
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Left: The dried blade of Porphyra perforata, a membranous red alga from the rocky intertidal zone of southern California. In Japan, species of Porphyra called "nori" are cultivated for food. Right: Crackers wrapped in nori and package of nori sheets used for wrapping sushi.
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The most extensively cultivated species of algae in the world belong to the genus Porphyra in the red algal division Rhodophyta. Porphyra includes many species of intertidal algae with broad, ruffled blades that are thin and membranous. The blades are collected as a popular Asian food known as "nori." In Japan, nori is typically cultivated in shallow muddy bays along the coast. At low tide during autumn, thousands of bamboo poles are driven into the mud, and miles of coarse-mesh netting are strung on the poles so they are exposed at low tide. Porphyra spores germinate on the netting and grow into harvestable plants in a few months. After harvesting, the nori is chopped into small fragments, spread over porous mats, and dried into thin sheets which are packaged for the market. According to E. Yale Dawson (Marine Botany, 1966), up to 2.5 billion dried sheets are produced in a single year from 133,000 tons of nori. Nori is used extensively in Asian countries as food. In fact, one of the most widespread and popular uses for nori is the dark outer wrapping of sushi.
Like other members of the algae, fungi and plant kingdoms, Porphyra has a separate haploid gametophyte and diploid sporophyte generation in its life cycle. This plant phenomenon known as the alternation of generations is taught in every introductory botany class. The gametophyte of Porphyra is the conspicuous alga harvested in Japan for nori, while the sporophyte is reduced to a minute filamentous form that appears like a small rosy patch inside sea shells. These small "plants" were formerly known under the genus name of Conchocelis. In 1950, Dr. Kathleen Drew worked out this unusual algal life history in her laboratory in Manchester, England. Until that time, no one knew where the spores came from that seeded the elaborate nets used by nori fishermen in Japan. The conchocelis stage of Porphyra is now grown commercially in oyster shells and used in "seeding" the nori plantations in shallow bays. To commemorate Dr. Drew's significant discovery, a monument was erected in her honor on the shores of Tokyo Bay overlooking the nori beds.
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Note: For more details about the remarkable alternation of generations and cultivation of nori, refer to chapter 19 of the recommended textbook for this course: Economic Botany: Plants In Our World by B.B. Simpson and M.C. Ogorzaly, 1995.
An alternations of generations also occurs in familiar plants in our everyday lives. In ferns, the diploid sporophyte plant is the typical, spore-bearing fern that we see in cultivated flower beds and in moist areas throughout North America. The haploid fern gametophyte is a small, seldom-seen, thallus plant about the size of your smallest fingernail. It superficially resembles a small green algal thallus (see photo link below). The gametophyte grows on the moist ground beneath sporophyte fern populations in areas with sufficient rainfall. Even flowering plants have a conspicuous sporophyte generation that alternates with a microscopic gametophyte phase within the ovule. The gametophyte phase is reduced to a 7-celled, egg-bearing embryo sac within the ovule, and a germinated pollen grain and sperm-bearing pollen tube.
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"Irish moss" (Chondrus crispus), a slimy red alga harvested from intertidal waters of the North Atlantic in Europe and North America. This species is an important commercial source of the thickening agent carrageenan.
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The mucilaginous red alga called "Irish moss" (Chondrus crispus) is the source of carrageenan (from the Irish "carrageen", meaning rock moss). Another important commercial source is the red alga Eucheuma from the Philippines. Most Irish moss is harvested from the North Atlantic coasts of the United States and Canada. It is especially abundant along beaches after hurricanes. According to E. Yale Dawson (Marine Botany, 1966), 10 million pounds of Irish moss are processed annually in Rockland, Maine. Carrageenans are hydrophilic (water-loving) polysaccharides closely related to gums. Like gums, they absorb water and are used as thickening agents, emulsifiers and to prevent the formation of ice crystals in frozen deserts. They are also referred to as phycocolloids because they come from algae (phyco) and they form jelly-like, colloidal suspensions in water. Carrageenan is especially valuable because it reverses its state when heated to a liquid and then cooled back to a gel. When added to hot milk and cooled, bonds are formed between the carrageenan and casein protein molecules in the milk, thus creating a thick, creamy texture. For this unique property carrageenans are used in many foods and pharmaceutical products, including chocolate toppings, jellies, frostings, milk puddings (blancmanges), yogurts, eggnog mixes, ice creams, sherbets, whipped cream, creamed soups, surgical jellies, salves, ointments, and toothpastes. It is also used as a sizing agent in the textile and leather industries, and as an emulsifier in oil-based printing inks.
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