Rhodophyta constitutes for a large majority of the seaweeds. They contain chlorophyll a together with blue and red pigments called phycobylins. They are mostly purple-red and red in colour but some species are brown or green and are therefore easily confused with chlorophyta and phaeophyta. The colour of the intertidal species range from green to reddish brown. They are often tough and wiry and much-branched to withstand the force of the waves. The deep-water forms are usually purplish-red: the blue-green light that penetrates deepest into the water is captured by their phycobylins and the energy is then passed on to the chlorophyll for photosynthesis to take place. Most of the algae grow in the form of flat sheets for the maximum absorption of light, but they are often rippled and flexible. Many species that have delicate branching blades grow epiphytically on other species of algae to hold them up to the light like the ferns and creepers in a forest.
The life cycles of the rhodophyta vary extremely but it usually consists of three distinct phases: The Sporophyte is called the tetrasporophyte since it produces spores in groups of four. These tetraspores develop into male and female gametophytes. On the mature female gametophytes distinctive knobbles are formed. In some groups the gametophyte and the sporophyte generations are alike. In other species the tetrasporophytes are smooth and groups of spores are visible only as small dark spots, while the gametophytes are more branched and with many papillae on the surface.