Monera ( ) is a kingdom that contains unicellular organisms with a prokaryotic cell organization, (having no nuclear membrane), such as bacteria. The taxon Monera was first proposed as a phylum by Ernst Haeckel in 1866. Subsequently, the phylum was elevated to the rank of kingdom in 1925 by Édouard Chatton. The last commonly accepted mega-classification with the taxon Monera was the five-kingdom classification system established by Robert Whittaker in 1969. Under the three-domain system of taxonomy, introduced by Carl Woese in 1977, which reflects the evolutionary history of life, the organisms found in kingdom Monera have been divided into two domains, Archaea and Bacteria (with Eukarya as the third domain). Furthermore the taxon Monera is paraphyletic (not all members descended from their most recent common ancestor), as Archaea and Eukarya are currently believed to be more closely related than either is to Bacteria. The term “moneran” is the informal name of members of this group and is still sometimes used (as is the term “prokaryote”) to denote a member of either domain. Most bacteria were classified under Monera; however, Cyanobacteria (often called the blue-green algae) were initially classified under Plantae due to their ability to photosynthesize.
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