Algae and seaweeds:Algae are not true plants.They form a diverse group of plantlike organisms that belong to the kingdom Protista. Like plants, algae possess the green pigment chlorophyll and make their own food by photosynthesis (see pp. 138-139). Many algae also possess other pigments by which they can be classified; for example, the brown pigment fucoxanthin is found in the brown algae. Some of the 10 phyla of algae are exclusively unicellular (single-celled); others also contain
aggregates of cells in filaments or colonies. Three phyla— the Chlorophyta (green algae), Rhodophyta (red algae), and Phaeophyta (brown algae)—contain larger, multicellular, thalloid (flat), marine organisms commonly known as seaweeds. Most algae can reproduce sexually. For example, in the brown seaweed Fucus vesiculosus, gametes (sex cells) are produced in conceptacles (chambers) in the receptacles (fertile tips of fronds); after their release into the sea, antherozoids (male gametes) and oospheres (female gametes) fuse; the resulting zygote settles on a rock and develops into a new seaweed.
