Silva, Paul C. Department of Botany, University of California, Berkeley, California.
Moe, Richard L. Department of Botany, University of California, Berkeley, California.
A division of the plant kingdom (also known as Chromophyta) comprising nine classes of algae: Bacillariophyceae (diatoms), Chrysophyceae (golden or golden-brown algae), Cryptophyceae, Dinophyceae (dinoflagellates), Eustigmatophyceae, Phaeophyceae (brown algae), Prymnesiophyceae, Raphidophyceae, and Xanthophyceae (yellow-green algae). Some of these classes are closely related, while others stand so far apart that they are sometimes assigned to their own divisions. The chief unifying character is the presence of chlorophyll c rather than chlorophyll b as a complement to chlorophyll a (although only chlorophyll a is present in Eustigmatophyceae). The chloroplasts are usually brown or yellowish because of large amounts of β-carotene and various xanthophylls, many of which are restricted to one or more classes. Storage products include lipids, starch, and glucans (glucose polymers with β-1,3 linkages). In all classes except Dinophyceae, the chloroplast is surrounded by chloroplast endoplasmic reticulum that is continuous with the nuclear envelope, and the deoxyribonucleic acid of the chloroplast forms an annular genophore. Except in Cryptophyceae, thylakoids are in groups of three. In most classes, motile cells bear two unequal flagella, one of which may be almost completely reduced and at least one of which bears two rows of hairlike appendages. Algae in this division range in size and complexity from unicellular flagellates to gigantic kelps. See also: Algae; Bacillariophyceae; Chrysophyceae; Cryptophyceae; Dinophyceae; Eustigmatophyceae; Phaeophyceae; Prymnesiophyceae; Raphidophyceae; Xanthophyceae
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