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Fucoidans is also the group of sulfated hetero- and homopolysaccharides especially in the cell wall of brown algae. Compositionally, simple fucoidans is homofucans which composed of only L-fucose residues (Figure 2.2C). Some studies have been also reviewed that fucoidans is fucose containing heteropolysaccharides with complex structures. The group of fucoidans polysaccharides are ranging from the compounds having high amount of uronic acids and low amount of fucose sugar. Further, the fucoidans also have mannose, xylose, galactose, uronic acid along acetyl factionalized. Sulfated homofucans is exclusively composed of sulfated fucopyranose with small content >10% of other sugars such as, D-mannose, D-xylose, D-galactose and very small content of uronic acid. Other hand, the heterogenous sulfated fucans is consist of sargassans and ascophyllans with small amount of fucose. In another heterogenous fucans polysaccharides have galactose and fructose with equivalent amount, thus known as galactofucans and fructofucans, respectively. Although, the fucoidans polysaccharides have not been found in other algal species and vascular plants, but fucan sulfates present in some marine echinoderms but its unlike that of algal fucoidans [32, 38].

Functionally, fucoidans help in algal cell wall formation by supporting their structures. It also contributes in gametes formation from reproductive organs and extrusion spores. The presence of sulfonate group in fucoidans polysaccharides, it contributes exchanging of divalent cations such as, Ca²⁺, Mg²⁺, Na⁺, etc. with environments by adjusting the algae with high concentration of salts and toxic effects of the heavy metals. It also plays pivotal role in zygote morphogenesis of fucoid algae [39].