What are the structural features of multicellular algae?

Algae is the oldest group of plants. They populated ponds, tree trunks, rocks and snow. These creatures belong to the lower ones, since they do not have in their structure those parts of the body that are present in higher plants. These include the stem, root, leaves, flowers and fruits. Instead of all this, their body is represented by one organ, this thallus. This body performs all the functions that are characteristic of all plants; it uses the energy of solar radiation to form oxygen and organic matter.