Whittaker's system placed most single celled organisms into either the Monera (prokaryotes—bacteria and blue-green algae) or the Protista (eukaryotes).
The history of the classification of bacteria and archaebacteria, and the use of the category Monera, reveals the nature of taxonomy (like science) to be dynamic, including clashes of doctrine and competing groups.
At times, four phyla of Kingdom Monera were recognized: Archaebacteria, Schizopyta (bacteria), Cyanophyta (the phytosynthetic cyanobacteria), and Prochlorophyta (symbiotic photosynthetic bacteria).
Based on molecular phylogeny studies, Woese proposed that the prokaryotes (monerans) be divided into two separate groups: Bacteria and Archaea.
Kingdom Monera historically included the bacteria, blue-green algae (cyanobacteria or blue-green bacteria), and the archaebacteria (Towle 1989).
Later, Haeckel proposed a fourth kingdom, which he called Monera.
Recently, this has manifested in a taxonomy where both Monera and, to a degree, the kingdom system are considered obsolete.
Monera, in some systems of biological classification, is a kingdom that comprises most living things with a prokaryotic cell organization.