Plant
Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom. The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the brown, red and green algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, and they are no longer classified as plants as defined here.
Wrack (seaweed)
It consists largely of species of "Fucus" — brown seaweeds with flat branched ribbon-like fronds, characterized in "F. serratus" by a saw-toothed margin and in "F. vesiculosus", another common species, by bearing air-bladders. Another component of sea wrack may be seagrasses such as "Zostera marina" a marine flowering plant with bright green long narrow grass-like leaves. "Posidonia australis", which occurs sub-tidally on the southern coasts of Australia, sheds its older ribbon-like leaf blades in winter, resulting in thick accumulations along more sheltered shorelines.Historically wrack was used for making manure, and for making "kelp", a form of potash.