Detailed Summary of Phaeophyceae
Phaeophyceae, commonly known as brown algae, predominantly inhabit marine environments. They exhibit remarkable diversity in size and structure, from simple filamentous forms like Ectocarpus to the gigantic kelps that can reach heights of up to 100 meters. Key pigments in brown algae include chlorophyll a, chlorophyll c, carotenoids, and xanthophylls like fucoxanthin, which give them their characteristic brown color.
Their nutritional strategy involves storing food in the form of complex carbohydrates such as laminarin and mannitol. The composition of their cell walls typically includes cellulose, often covered by a gelatinous coating of algin. The vegetative structure of brown algae consists of a holdfast that anchors them to a substrate, a stipe that acts like a stem, and fronds that perform photosynthesis.
Reproduction in Phaeophyceae is varied: vegetative reproduction occurs through fragmentation; asexual reproduction is primarily via biflagellate zoospores, which are flagellated and have two unequal flagella; sexual reproduction can be isogamous, anisogamous, or oogamous. In oogamous species, gametes can fuse in water or within a specialized structure called the oogonium. Key genera include Ectocarpus, Laminaria, Sargassum, and Fucus.