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a class of red algae (division Rhoidophyta). The multicellular thalli, which may be microscopic or measure as much as 0.5 m in height, consist of a single row of cells or of complex tissue structure. They may be filamentous, lamellar, or bushy and are sometimes divided into a stem and leaflike organs. In several of the Florideophyceae, for example, the genus Lithothamnion, the thalli are hard owing to deposits of calcium salts. The cells of Florideophyceae have evident plasmodesmata.
The growth cycle consists in alternating generations of sporophytes and gametophytes. The sporophytes, which are usually diploid, produce tetraspores or sometimes monospores or poly-spores. In the gametophytes, after fertilization, filaments bearing the carpospores grow from the carpogonium, either directly or from special connected cells.
The class includes approximately 540 genera, with 3,700 species, all but a few of which are marine species. Some species parasitize other members of the class. Several members of the Florideophyceae are used for the production of gelatin-forming substances and for medical purposes.