PHAEOPHYCEAE (Brown Algae)

• Plant body is colonial, motile, non-motile, unbranched, filamentous immobile, multicellular and highly differentiated both externally and internally.
• It is characterised by the presence of golden brown xanthophylls pigment fucoxanthin which gives olive green color. Pigments lie in chromatophores.
• The reserve food is laminarin and mannitol. Laminarin is present in maximum quantity.
• The growth of plant body may be apical (Fucales, Dictyotales) intercalary (Laminariales) or tricothallic in (Ectocarpales.)
• Most phaeophytes are lithophytes attached to rocks with the help of holdfast.
• Main pigment are chlorophyll a, chlorophyll c, and other xanthophylls.
• Cell wall has two layers. The inner layer consists of cellulose and outer layer is gelatinous and is composed of pectin.
• In metabolically active regions fucosan vesicles  are found in cytoplasm
• Most of members the outer layers contains colloidal substance like algin and fucoidin which are of great economic importance.
• Cells are uninucleate with comparatively larger nucleus.
• Brown algae have all the three type of reproduction i.e. Vegetative, asexual, and sexual.
• Vegetative reproduction is by fragmentation e. g.  Saragassum natans while in Sphacelaria it by formation of propagules.
• Asexual reproduction is found in all genera of phaeophyceae except Sargassum and fucus.  It is by means of motile or non-motile spores formed in unilocular sporangia (Ectocarpus) plurilocular or neutral sporangia (Ectocarpus) or by tetrasporangia (Dictyota).
• Sexual reproduction are diploid except (Fucales). It ranges from isogamy to anisogamy to oogamy.
• The members shows various type of alternation of generation i.e. Isomorphic (Ectocarpus), heteromorphic in (Laminaria), Or diplontic (Sargassum).

Classification of Phaeophyceae (Brown Algae)

According to Fritsch

He classified the Phaeophyceae into nine orders.

Orders

1.  Ectocarpales e.g. (Ectocarpus, Haiothrix)
2. Cutleriales e.g. (Cutlria)
3. Fucales e.g. (Sargassum)
4. Dictyotales e.g. (Dictyota)
5. Laminariales e.g. (Laminaria)
6.  Desmarestiales e.g. (Desmarestia)
7.  Sporochnales e.g.  (Sporochnus)
8. Tilopteridales e.g. (Ptilopteris)
9. Sphacelariales e.g. (Sphacelaria).