Red algae are an ancient group of primarily marine organisms.
They are a species-rich group - with some 7000 species worldwide, they have more than the green and brown seaweeds combined. This richness is reflected in the complexity and diversity of red algal morphology and anatomy.
As red algae often lack conspicuous morphological features and have complex life histories, phycologists use additional characteristics to distinguish between species and to draw conclusions about taxonomic relationships.
Different approaches include anatomical, biochemical and physiological studies. However it is molecular studies over the last decade that have profoundly changed our notions of red algal classification - and indeed seaweed classification - at all levels.