Gibbons and Murray, 1978: Procaryotes having a gram-positive type of cell wall. Reproduction mainly by binary fission. Cells may be spheres, rods, or filaments; the filaments may be branching or nonbranching. Some form endospores; some produce spores on hyphae or in sporangia. Some are motile by means of flagella; the majority are nonmotile. These organisms may be aerobic, anaerobic, or facultatively anaerobic.
Several orders that cover some of the groups in this division are listed in Index Bergeyana. Actinomycetales Buchanan 1917, 162 was the only order provided by the authors of the 8th edition of the Manual, and it might be considered the type order on the basis of priority. However, Bacillales Pribram 1933, 79 is proposed as the type order, based on the priority of the genus Bacillus Cohn 1972 over Actinomyces Harz 1877. It is also a more typical representative of gram-positive organisms.
Oren and Garrity, 2021: The properties of the taxon are as described by Gibbons and Murray, 1978. Effectively published synonyms: Firmacutes Gibbons and Murray 1978; Firmicutes corrig. Murray 1984. Type genus: Bacillus Cohn 1872 (Approved Lists 1980).