General features of class phaeophyceae:
They are called brown algae, few live in freshwater and majority live in sea water. The body of plant varies from simple branched filaments to large leathery branched structures with highly differentiated thallus.
Unicellular, colonial or un-branched filamentous forms are not found in this class. There is interval differentiation of thallus into epidermis, cortex and medulla. The cell has usually two layered cell wall, primordial utricle, a nucleus and chromatophorus without pyrenoids.
Plants are brown in coloure due to presence of fucoxanthin in addition to chlorophyll. There are also present highly retractive colourless fucosan vesicles. Food reserve is found in the form of soluble complex carbohydrate like laminarin, mannitol and fat instead of starch.
Reproduction takes place by vegetative, asexual or sexual methods. Vegetative reproduction takes place by frognuentation.
Asexual reproduction takes place by pear-shaped zoospores or naked aplanospores except order fucales.
1. Sexual reproduction takes place by isogamy and oogamy. Reproductive structures have two unequal laterally instead cilia. There is definite alternation of generation except order fucales.
Classification: It is based as structure, reproduction and life histories,
Kylin (1933), Fritsch (1935), Pappenfus (1947) and Smith (1955) worked on classification.
(i) Kylin in 1933 divided phaeophyceae into two subclasses (A) Iso-generate – includes five orders
(B) Heterogenerate – includes four orders.
2. Pappenfus in 1947 included one more subclass cyclosporae which includes one order fucales.
3. Smith in 1955 gavea detailed classification based on above said workers.
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