Bacteria and Archaea Domain Eukaryota Monera (/məˈnɪərə/) (Greek: μονήρης (monḗrēs), "single", "solitary") is historically a biological kingdom that is made up of prokaryotes.

Furthermore, the taxon Monera is paraphyletic (does not include all descendants of their most recent common ancestor), as Archaea and Eukarya are currently believed to be more closely related than either is to Bacteria.

[6][7][8] Seven years after The Origin of Species by Charles Darwin, in 1866 Ernst Haeckel, a supporter of evolutionary theory, proposed a three-kingdom system that added the Protista as a new kingdom that contained most microscopic organisms.

[2] One of his eight major divisions of Protista was composed of the monerans (called Moneres by Haeckel), which he defined as completely structure-less and homogeneous organisms, consisting only of a piece of plasma.

Furthermore, Haeckel's classification lacked specificity and was not exhaustive — it in fact covers only a few pages—, consequently a lot of confusion arose even to the point that the Monera did not contain bacterial genera and others according to Huxley.

[23] The anthropic importance of the crown group of animals, plants and fungi was hard to depose; consequently, several other megaclassification schemes ignored on the empire rank but maintained the kingdom Monera consisting of bacteria, such Copeland in 1938 and Whittaker in 1969.

[25] Whittaker subdivided the kingdom into two branches containing several phyla: Alternative commonly followed subdivision systems were based on Gram stains.

This culminated in the Gibbons and Murray classification of 1978:[26] In 1977, a PNAS paper by Carl Woese and George Fox demonstrated that the archaea (initially called archaebacteria) are not significantly closer in relationship to the bacteria than they are to eukaryotes.

[30] Although it was generally accepted that one could distinguish prokaryotes from eukaryotes on the basis of the presence of a nucleus, mitosis versus binary fission as a way of reproducing, size, and other traits, the monophyly of the kingdom Monera (or for that matter, whether classification should be according to phylogeny) was controversial for many decades.

In 1974, the influential Bergey's Manual published a new edition coining the term cyanobacteria to refer to what had been called blue-green algae, marking the acceptance of this group within the Monera.