Cyanoprokaryotes are probably the oldest organisms with oxygen generating photosynthesis. However, their cell structure and type of asexual reproduction prove their eubacterial origin. This volume treats cyanobacterial types with diversified thalli, with the typical presence of prominent, specialized cells having specific functions (heterocytes, akinetes, hairs, necridia), complex life cycles, and a combination of various reproductive strategies (monocytes, hormogonia and hormocytes). The most diversified heterocytous cyanobacteria with multicellular, morphologically complex thalli have a specific position among prokaryotic organisms. It is the last part of a review of cyanoprokaryotes (Cyanophyta, Cyanobacteria) issued in the Susswasserflora von Mitteleuropa .

All heterocytous cyanobacteria are included in this volume, especially taxa studied and revised according to modern phylogenetic criteria. The author tried to respect all confirmed changes and corrections and stresses especially those morphological features that are not controversial to phylogenetic studies and enable the identification of various populations in nature or in cultures according to morphological characteristics. A synthesis of modern results with traditional nomenclature - sometimes difficult - is aimed to foster progress in cyanobacterial research. One of the major reasons to present this work is to enhance identification of natural populations using morphological criteria for their identification.