Aside from the obvious reddish color, red algae procure energy from photosynthesis, and unlike other algae species, lack flagella and centrioles. There are approximately 4,500 species of red algae, ranging from single-celled organisms to multi-celled seaweeds.
Dissimilar to other eukaryotic classifications, red algae chloroplasts do not contain an endoplasmic reticulum or unstacked thylakoids. Most red algae species are macroscopic, multicellular, capable of sexual reproduction and possess an alteration of generations.
The reddish color stems from the masking of chlorophyll by phycoerythrin and phycocyanin pigments. These pigments absorb blue light and reflect red light to produce a reddish hue. This distinct color is an evolutionary mechanism, which allows red algae to thrive at greater depths relative to other types of algae.
Red algae are common to tropical and subtropical environments. Most species are slender in appearance, but connect and branch to one another to form sprawling shrub-like bodies. Depending on species, red algae can contain feathered, branched, flat or filamentous cells.
The majority of red algae species secrete calcium carbonate and play a vital role in constructing coral reefs. Certain red algae species, such as Nori, serve as a fundamental food source, while other species, such as Irish moss, serve as a thickener or preserve for toothpaste, ice cream, pudding and an assortment of other foods and drinks.