Actinomycetales
Scanning electron micrograph of Actinomyces israelii.
Scientific classification
Kingdom:	Bacteria
Phylum:	Actinobacteria
Class:	Actinobacteria
Subclass:	Actinobacteridae
Order:	Actinomycetales Buchanan, 1917
Suborders/Families
Actinomycineae Actinomycetaceae Actinopolysporineae Actinopolysporaceae Catenulisporineae Catenulisporaceae Actinospicaceae Corynebacterineae  ?Tomitella  ?Hoyosella Corynebacteriaceae Dietziaceae Gordoniaceae Mycobacteriaceae Nocardiaceae Segniliparaceae Tsukamurellaceae Frankineae Acidothermaceae Cryptosporangiaceae Frankiaceae Geodermatophilaceae Nakamurellaceae Sporichthyaceae Glycomycineae Glycomycetaceae Jiangellineae Jiangellaceae Kineosporiineae Kineosporiaceae Micrococcineae  ?Koreibacter  ?Luteimicrobium Beutenbergiaceae Bogoriellaceae Brevibacteriaceae Cellulomonadaceae Demequinaceae Dermabacteraceae Dermatophilaceae Dermacoccaceae Intrasporangiaceae Jonesiaceae Microbacteriaceae Micrococcaceae Promicromonosporaceae Rarobacteraceae Ruaniaceae Sanguibacteraceae Micromonosporineae Micromonosporaceae Propionibacterineae Nocardioidaceae Propionibacteriaceae Pseudonocardineae Pseudonocardiaceae Streptomycineae Streptomycetaceae Streptosporangineae  ?Sinosporangium Nocardiopsaceae Streptosporangiaceae Thermomonosporaceae

Actinomycetales is an order of Actinobacteria. They are very diverse and contain a variety of subdivisions as well as yet-unclassified isolates. This is mainly because some genera are very difficult to classify because of a highly niche-dependent phenotype. For example Nocardia contains several phenotypes that were first believed to be distinct species before it was proven that their differences are entirely dependent on their growth conditions.

Why is Classification difficult

Actinomycetales are Gram-positive, however several species have complex cell wall structures that make the gram staining unsuitable. Examples: Mycobacteriaceae

References

• See the NCBI webpage on Actinomycetales Data extracted from the "NCBI Taxonomy Browser". National Center for Biotechnology Information. http://www.ncbi.nlm.nih.gov/Taxonomy/taxonomyhome.html/index.cgi. Retrieved 2011-06-05. 
• J.P. Euzéby. "Actinomycetales". List of Prokaryotic names with Standing in Nomenclature. Archived from the original on 13 June 2011. http://www.bacterio.cict.fr/classifphyla.html#Actinobacteria. Retrieved 2011-06-11. 
• Labeda et al. (2011). "Abstract of Reassessment of the systematics of the suborder Pseudonocardineae: transfer of the genera within the family Actinosynnemataceae Labeda and Kroppenstedt 2000 emend. Zhi et al. 2009 into an emended family Pseudonocardiaceae Embley et al. 1989 emend. Zhi et al. 2009". International Journal of Systematic Evolutionary Microbiology vol. 61. pp. 1259–1264. http://ijs.sgmjournals.org/content/61/6/1259. Retrieved 2011-06-11.