Phaeophyceae: Brown Algae The brown colour of these algae
results from the dominance of the xanthophyll pigment
fucoxanthin, which masks the other pigments, Chlorophyll a and c
(there is no Chlorophyll b), beta-carotene and other
xanthophylls. Food reserves are typically complex
polysaccharides, sugars and higher alcohols. The principal
carbohydrate reserve is laminaran, and true starch is absent
(compare with the green algae). The walls are made of cellulose
and alginic acid, a long-chained heteropolysaccharide. There are
no known unicellular or colonial representatives; the simplest
plant form is a branched, filamentous thallus. The kelps are the
largest (up to 70 m long) and perhaps the most complex brown
algae, and they are the only algae known to have internal tissue
differentiation into conducting tissue; there is, however, no
true xylem tissue as found in the ‘higher’ plants. Most brown
algae have an alternation of haploid and diploid generations.
The haploid thalli form isogamous, anisogamous or oogam