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Page 3 Golden Algae Chrysophytes are a large and complex group characterized by plastids containing distinctive golden yellow pigments. The group is diverse in form, yet all feature this yellow color, permitting easy iden- tification. Chrysophytes are usually found in cold freshwater lakes and ponds, although some marine forms are common. Synura, existing in colonies in fresh water, can cause a fishy odor in reservoirs even in low concentrations, but is not harmful. Green Algae Chlorophytes are a diverse group and are common in fresh water, salt water, and soil. They are very similar to plants, and most botanists agree the ancestor of higher plants can be found somewhere within this group. Chlorophyte reproduction varies greatly, from asexual division to isogamy and heterogamy to oogamy. Cell walls are constructed of cellulose and pectin. The food storage product is true starch, the same as plants. This can be demonstrated by staining with KI, which turns the starch in the algae blue-black. Green algae possess true chloroplasts, which contain the same pigments found in higher plants: chlorophyll a and b, alpha and beta carotene, and many xanthophylls. Red Algae Although Rhodophytes, the most abundant type of seaweed, are widely distributed in the oceans, most occur in tropical and subtropical littoral zones. Of the 4,000 species, the vast majority are marine. Rhodophytes are not mobile — they possess no flagellated or ciliated cells at any stage of their life cycle — yet all reproduce sexually. Many red algae, such as Corallina, are calcified and encrusted appearing much like coral. This calcification has made it possible to trace the Rhodophytes to the Paleozoic Period. Single-celled forms such as Porphyridium are a rarity. Rhodophytes are characterized by reddish plastids, called rhodoplasts, which contain the pigments chlorophyll a and d, alpha and beta carotene, some xanthophylls and phycobiliproteins. Yellow-Green Algae Xanthophytes are highly successful in fresh water and terrestrial environments, although some marine forms also exist. The yellow-green algae have pectin-rich cellulose walls. Starch is absent and food is stored in the form of oils. Xanthophytes are characterized by yellow-green plastids (xanthoplasts) which contain pigments chlorophyll a and c, several xanthins, and beta carotene. Vaucheria is a large macroscopic, filamentous form that was classified a chlorophyte until pigment analysis showed the absence of chlorophyll b and true starch. Tribonema is a typical freshwater, unbranched, filamentous form which clearly demonstrates overlapping walls. Blue-Green Algae (Cyanobacteria) The cyanophytes are the only prokaryotic algae. They are found in virtually every type of environment including terrestrial, freshwater, and marine habitats. Since cyanobacteria are prokaryotes, they lack membrane bound organelles. However, the external structure can range from unicellular or colonial to branched or unbranched and filamentous. Like the rhodophytes, the cyanophytes possess no flagel- lated or cilliated cells at any stage of their lifecycle, although, simple movements such as bending and swaying are made possible by internal pressure changes exerted on the cell wall. They are heavily pigmented with chlorophyll a, beta carotene, and several xanthophylls. The presence of several phycobiliproteins gives the cyanophyta their unique blue-green coloration. Food is stored in the form of glycogen.