Red algae have a number of general characteristics that in combination distinguish them from other eukaryotic groups:

• absence of flagella and centrioles
• floridean starch as a storage product and the storage of starch in the cytoplasm (Figure 2)
• phycoerythrin, phycocyanin, and allophycocyanin as accessory pigments
• unstacked thylakoids in plastids (Figure 3)
• no chloroplast endoplasmic reticulum

Figure 2. Griffithsia pacifica (Florideophyceae). Electron micrograph showing cytoplasm with numerous chloroplasts (C) and starch (S). Starch is the photosynthetic reserve and is deposited free in the cytoplasm.
Image copyright © 2000, C. M. Pueschel.

Figure 3. Griffithsia pacifica (Florideophyceae). Close-up of figure 2 electron micrograph showing a chloroplast with unstacked photosynthetic lamellae (arrows) bearing granules, called phycobilosomes (arrowheads), composed of water-soluble phycobiliprotein accessory pigments.
Image copyright © 2000, C. M. Pueschel.