Phaeophyta: The Brown Algae

Figure 14-1 A biflagellated gamete showing an anterior tinsel-type flagellum and a posteriorly directed whiplash flagellum.

There is great variation among Phaeophyta, the brown algae. A few are microscopically sized, most are conspicuous, and some can reach lengths of more than 150 feet. The large brown algae are called kelp. Pigments in the brown algae are chlorophyll a, chlorophyll c, beta-carotene, xanthophylls, and fucoxanthin, a pigment that gets its name from the brown alga Fucus and is not found elsewhere. The pigments are contained in plastids. The cell wall has an inner cellulose layer and an outer gelatinous coat composed mainly of algin, which has a number of commercial uses (noted in a following section). The product of photosynthesis in many brown algae is a soluble polysaccharide called laminarin. Alternation of generations occurs in the life cycles of brown algae except those of the order Fucales. The motile reproductive cells are distinctive, being laterally biflagellated. A longer flagellum extends anteriorly, and a shorter one extends posteriorly. While the anterior flagellum is tinsel typet, he posterior one is not. In the Fucales order, this arrangement is reversed.