Green algae usually appear in green because they contain the same ratio of chlorophyll a and b as that of higher plants. Their photosynthetic products are starch and their cell walls are mainly composed of cellulose. Hence, it is generally believed that green algae are closely related to terrestrial higher plants in the theory of biological evolution.
Marine green algae can usually be found in the littoral zone where there is strong sunlight. They have various forms of chloroplasts. For instance, their plastids may appear to be cup-shape, net-like, stellate-shap, plate, disc-liked, annulus or spiral.The forms, numbers and positions of these plastids are important characters used in the taxonomy of green algae. From external morphology, green algae may appear to be filamentous, membranous, cylindrical, globular or coenocytic, depending on the way their cell divisions. For example, cells of a filamentous species usually divide in one direction and the divided cells either connect one another in a string or become dichotomous filamentous. Typical examples include Chaetomorphaantennina and Boodlea composita.Membranous cells divide laterally to form flaky structures, such as Ulva lactuca,Ulva compressa and Anadyomene wrightii. Some cells only undergo mitosis (division of nucleus) but do not undergo cytokinesis (division of cytoplasm). These cells only perform nuclear divisions to form unicellular coenocytic structures, such as Boergesenia forbesii, Codiumarabicum, Bryopsisplumosa, Caulerpabrachypus f. parvifolia and Parvocaulisparvula.
Green algae reproduce in many different ways. Asexual reproduction includes a variety of schizogenesis and sporogony; sexual reproduction includes isogamy and heterogamy. Alternation of generation is obvious in most macroalgae. For instance, the gametophyte and sporophyte of Ulvalactuca can grow independently. Hence, evolutionary biologists believe green algae and ferns share a common ancestor.
According to the investigation report released by UNFAO in 1976, among all algae used in food production and used for feed and fertilizer around the world, there are 35 types of marine green algae. Many green algae are used as traditional Chinese medicine. For examples, green algae may reduce fever, detoxicate the body, prevent the development of tumors, help reduce swelling and clear thick phlegm. For instance, “The Appendix to Compendium of Materia Medica” states, “Ulva lactuca ‘has favorable flavor, is modest and atoxic’”, “…is diuretic”. In the “Recipe of Sueisi Residence” we can find that “Enteromorpha prolifera may help to clear the gallbladder, to prevent the development of tumors, to reduce swelling, clear phlegm and to cure sickness caused by a different diet.” Contemporary analytical technology shows that green algae contain polysaccharides, protein, amino acid, starch, saccaride, acrylic acid, fatty acid, vitamins, mineral salts and trace elements. Animal experiments also prove that Monostroma nitidum and Enteromorphaprolifera can significantly reduce the amount of cholesterol in the blood of animals. Some Enteromorpha prolifera can help treat thyroid enlargement, cough, asthma, tracheitis, tonsillitis and nasal bleeding and can ease pain and reduce fever. Ulva pertusa and Ulva lactuca can be used to treat urological ailments and oedema. Parvocaulisparvula and Codium arabicum are good ascaricides. In the future, the development and application of natural seaweeds will facilitate the development of algae farming and vice versa. The potential of macro algae is unlimited.
There are 17 families, 34 genus and 113 species of marine green algae found in Taiwan. The taxonomy and check-list of seaweeds, please refer to the Seaweed Resources of Taiwan.