The Chloroflexia class is a group of deep branching photosynthetic bacteria (with the exception of Herpetosiphon and Kallotenue species) that currently consist of three orders: Chloroflexales, Herpetosiphonales, and Kallotenuales.

[1][5][6][7][8] The Herpetosiphonales and Kallotenuales each consist of a single genus within its own family, Herpetosiphonaceae (Herpetosiphon) and Kallotenuaceae (Kallotenue), respectively, whereas the Chloroflexales are more phylogenetically diverse.

[1] The revised taxonomy was based on the identification of a number of conserved signature indels (CSIs) which serve as highly reliable molecular markers of shared ancestry.

[18][19] Additional work has been done using CSIs to demarcate the phylogenetic position of Chloroflexia relative to other photosynthetic groups such as the Cyanobacteria.

As the two lineages are not otherwise closely related, the interpretation is that the CSIs are the result of a horizontal gene transfer event between the two.