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SUBKINGDOM ALGAE: 



occur in combination with fungi in a growth form 

 called a lichen. 



Being plants, the primary ecological role of algae is 

 production of food, naturally, by photosynthesis. In 

 fulfilling this role algae are most important in aquatic 

 situations — at least they are the most abundant and 

 widespread plants there. Green algae occur in all 

 seas and in most fresh-water habitats. They are most 

 numerous and probably influential in fresh water. 

 Many occur in moist land environments (e.g., some 

 grow upon rocks, trees, ice or snow). Red snow is 

 caused by greens that have a red pigment masking 

 their chlorophyll. Some even grow upon animals 

 and plants. With blue-green algae, a few provide 

 external coloring to arboreal animals. Many aquatic 

 species also color the eggs, larvae, or adults of aquatic 

 animals. For example, some fresh-water greens, add 

 color to, apparently gain carbon dioxide from, and 

 perhaps provide greater oxygen to the eggs of certain 

 amphibians. Such algae usually are not parasites, 

 they generally use the host organism merely as a site 

 of attachment. However, some green algae are plant, 

 especially leaf, parasites. 



Diatoms are microscopic. In both fresh and salt 

 water, with certain flagellates, they usually are so 

 numerous as to be the primary food-producing or- 

 ganisms in their habitat. For this reason, aquatic 

 animals often are dependent upon the existence of 

 these plants. Some diatoms can survive in perpetual 

 darkness if certain simple, organic compounds (e.g., 

 glucose) are present. Such species live heterotrophi- 

 cally. At least one species (.\ilZH'fiia f/iitrtda) lacks 

 chlorophyll, hence must always live by heterotrophic 

 means. In addition, probably all extract silica from 

 their aquatic medium to construct a two-part cell 

 wall, or shell, reminiscent of the two halves of a pill 

 box (one "box" fits tightly within the other). There- 

 fore, when diatoms die their silica shells accumulate 

 to form diatomaceous ooze; upon compaction, the 

 ooze becomes a rock called "diatomaceous earth" or 

 "diatomite." 



Brown algae are almost exclusively marine; in fact, 

 there is disagreement as to whether the so-called 

 fresh-water forms are indeed brown algae. They 

 include the largest algae; some surpass 100 feet in 

 length. All sizes can be found in all oceans but 

 browns are especially abundant in cold and temper- 

 ate seas of the Northern Hemisphere. Near many 

 coasts, they are the most abundant and conspicuous 

 plants. Here, they often form extensive "forests," 

 kelp beds. 



About 7 per cent of the red algae occur in fresh 

 water; the rest probably are marine. They are most 

 numerous in subtropical and tropical waters but 

 extend to depths of maximum light penetration in all 

 seas, often to the 600-foot level. Species occurring 

 in fresh and intertidal waters are less likely to be red 

 than are the deep-sea forms. In addition to being 

 food producers, additional ecological significance 

 comes from the coraline red algae. These plants are 

 more significant calcium carbonate contributors to 

 reef formation than are corals. Some reds grow upon 

 others and a few of these appear semiparasitic. 



The marine algae normally have distributions 

 limited to particular latitudes, oceans, or coasts. For 

 this reason, one can speak of climatic, oceanic, or 

 regional algal floras. These plants generally have 

 structures and functions that enable survival in surf. 

 Also, many can withstand short periods of drying. 

 Partly for these reasons, marine forms are mostly 

 intertidal. 



Most fresh-water algae are cosmopolitan, owing to 

 dispersal by such things as winds and the muddy feet 

 of birds. However, light, temperature, and water 

 chemistry place some restriction upon their potential 

 ranges. The greatest number of individuals and 

 species exists in slightly alkaline, quiet waters that 

 are rich in such things as nitrates and phosphates. 

 Only a few species occur or are restricted to rapid- 

 moving fresh waters. Waters that are acid or poor 

 in nutrients also have few algae. 



The need for nutrients points out that algae are like 

 other plants. Different algae (in fact, different plants) 

 have unlike requirements in amounts and kinds of 

 vitamins, growth-promoting substances, and trace 

 elements. Many of these nutrients are synthesized by 

 bacteria or blue-green algae, some even by other true 

 algae. 



CHLOROPHYTA (Green Algae) 



Stnuture: typically cellular organization, but also 

 unicellular and independent or colonial; mostly grass- 

 green plants; unicellular forms mostly of fixed, oval to 

 spherical form; colonies of small cell clusters in the 

 form of discs, large and irregular masses, or hollow 

 spheres; multicellular structure of filaments (sirhple 

 and hair-like or branching), flat and thin sheets 

 (continuous or somewhat narrow and branching), 

 hollow tubes, or solid cylinders (simple to many- 

 branched to feather-like), and some resemble vascular 

 plants; those resembling vascular plants possess leaf, 



