A Kingdom Monera:
Some general features of monera are as follows.
Absence of a well-defined nucleus or membrane-bound organelles
Absence of multicellular body designs [All are unicellular.]
Presence or absence of a cell wall
Autotrophic or heterotrophic mode of nutrition
This kingdom includes mainly bacteria and blue-green algae (cyanobacteria).
All the bacteria were placed under the Kingdom Monera, according to R.H. Whittaker's five kingdom classification. All prokaryotes are grouped under kingdom Monera. Therefore, the other four kingdoms include only eukaryotes.
B Algae are unicellular prokaryotes. They lack nucleus and other membrane bound organelles like mitochondria, endoplasmic reticulum, etc. While kingdom plantae are multicellular eukaryotes. So, Algae can not be placed in kingdom plantae.