Glaucophyceae (Glaucophytes)

Glaucophyceae is a small, primitive group of freshwater algae that holds great evolutionary significance because it shows a direct link between cyanobacteria and modern plastids (chloroplasts).

General Characteristics of Glaucophyceae

• Primitive algal group with strong evolutionary importance
• Mostly unicellular, rarely colonial
• Freshwater habitat (ponds, lakes, slow-moving water)
• Cells generally non-motile
• Eukaryotic organisms (true nucleus present)
• Chloroplasts are unique and called cyanelles
• Cyanelles retain a peptidoglycan (murein) layer

Photosynthetic pigments:

• Chlorophyll a
• Phycobilins (phycocyanin, allophycocyanin)
• Chlorophyll b absent

• Cell wall mainly composed of cellulose
• Reserve food: cyanophycean starch (stored in cytoplasm)
• Asexual reproduction only, usually by binary fission
• Sexual reproduction absent
• Rare, less diverse, and considered living fossils

Mode of Reproduction

• Only asexual reproduction is present
• Sexual reproduction is completely absent

Asexual Reproduction

Occurs mainly by:

🔹 Binary Fission

• The most common method
• The parent cell divides mitotically into two identical daughter cells
• Each daughter cell receives:
  • One nucleus
  • Cyanelles (chloroplasts) by division
• Growth is slow but stable

Type of Life Cycle

• Asexual
• Monogenetic
• Haploid (n)

🧬 Stages of Life Cycle

1. Vegetative Cell (n)
   • The organism exists as a haploid unicellular body
   • Contains:
     • True nucleus
     • Cyanelles (chloroplast-like organelles)
2. Cell Growth
   • Cell increases in size
   • Cyanelles replicate by division
3. Binary Fission
   • Nucleus divides by mitosis
   • Cytoplasm divides
   • Two identical haploid daughter cells are formed
4. Independent Daughter Cells
   • Each daughter cell grows and repeats the same cycle

Evolutionary Importance of Glaucophyceae

Glaucophyceae occupy a key evolutionary position among algae because they preserve features that link prokaryotic cyanobacteria with eukaryotic chloroplasts.

Major Evolutionary Significance

• Living evidence of endosymbiosis
  • Their plastids (cyanelles) closely resemble cyanobacteria
  • Presence of a peptidoglycan (murein) layer between plastid membranes—absent in higher plants
• Bridge between prokaryotes and eukaryotes
  • Show transitional characters between:
    • Cyanobacteria (prokaryotes)
    • Chloroplasts of algae and higher plants (eukaryotes)
• Support to Endosymbiotic Theory
  • Cyanelles contain:
    • Circular DNA
    • 70S ribosomes
    • Division by fission
  • Strongly supports that chloroplasts evolved from engulfed cyanobacteria
• Primitive photosynthetic machinery
  • Pigments include chlorophyll a and phycobilins
  • Similar to cyanobacterial photosystems
• Ancestral plastid condition
  • Considered closest to the original plastid from which red algae, green algae, and land plant chloroplasts evolved
• Low diversification = ancient lineage
  • Limited species diversity suggests early divergence and long evolutionary stability