There is only one subfamily in the family.
Genus demarcation criteria
Genera are defined on the basis of DEmARC analysis of portions of their complete genome sequences. Genus demarcation is on the basis of analyses using DEmARC (DivErsity pArtitioning by hieRarchical Clustering) - a computational framework applied to all nidoviruses (Lauber and Gorbalenya 2012). DEmARC uses profiles of multiple sequence alignments of the 3CLpro, NiRAN, RdRP, ZBD and HEL1 domains, Bayesian and Maximum-likelihood phylogenetic trees, and profiles of clustering cost (CC) function that are produced for weighted hierarchical clustering of pairwise patristic distances (PPD). The species demarcation threshold is set as a range of PUD values (0.029%–0.043 %) which are deduced from PPD values for which the number of clusters (taxa) remained constant and the CC = 0. PUD values represent the % of different residues in compared proteins.
This demarcation derived from DEmARC analysis should also reflect significant differences in ecology and/or genome organisation between members assigned to different genera.