Seaweed: Rhodophyta

The Rhodophyta are a unique group of organisms, which, like the Chlorophyta, are thought to be very ancient. No cell, including reproductive cells, is ever flagellated. Like the Chlorophyta, the chloroplast is encircled by a double membrane, but thylakoids occur singly and are not stacked.

Only chlorophyll a is present, and cells are distinctively colored by the accessory pigments, phycocyanin and phycoerythrin, which occur in hemispheric granules on the thylakoids. The photosynthetic product is a highly branched form of starch and is stored outside the chloroplast. Most red algae belong to the Class Floideophyceae, which is characterized by proteinaceious "pit" plugs occluding the connection between cells (due to incomplete cell cleavage at mitosis). Most red algae are multicellular and marine, but unicellular and freshwater taxa also occur.