Red Algae Beach, Sydney, Australia

Calcite crusts, which have been interpreted as the remains of coralline red algae, date to the terminal Proterozoic. Thallophytes resembling coralline red algae are known from the late Proterozoic Doushantuo formation.
Taxonomy
In the system of Adl et al. 2005, the red algae are classified in the Archaeplastida, along with the glaucophytes and green algae plus land plants (Viridiplantae or Chloroplastida). The authors use a hierarchical arrangement where the clade names do not signify rank; the class name Rhodophyceae is used for the red algae. No subdivisions are given; the authors say, "Traditional subgroups are artificial constructs, and no longer valid."