Phylum Rhodophyta

Like brown algae, the red algae also contain complex forms, mostly marine, with elaborate life cycles. Chloroplasts in this group show pigments very similar to those found in cyanobacteria, and ancient red algae may have engulfed these cyanobacteria as endosymbionts. Red algae have many important commercial applications, such as the agar used for culture plates. Its cell walls contain carrageenan, a polysaccharide used in the manufacture of ice cream, paint, and cosmetics.