This order comprises only one family, the Ardeidae (herons, egrets, and bitterns).
Phylogeny of Ardeidae based on Hruska (2018), with the distribution of each taxon being indicated by the colour-code used throughout this website (see Distribution colour code). The cladogram shows that there are at least two separate groups of Night Herons within the Ardeinae. As a consequence, nocturnality either must have evolved or been lost at least twice. Likewise, the scattered distribution of migratory behaviour among members of the Botaurinae and Ardeinae suggests that it evolved or has been lost on multiple occasions.
Hruska, J.P. (2018), "A phylogenomic evaluation of the relationships among herons (Aves: Ardeidae)", Master's Thesis, University of Kansas. (pdf)
Liang, W.-L., J. Zhou, and Z.-M. Ren (2019), Complete mitochondrial genome of Ciconia nigra (Ciconiiformes: Ciconiidae), a threatened stork in China,
Mitochondrial DNA, Part B 2(2), 510-511. DOI 10.1080/23802359.2017.1640082. (pdf)
Päckert, M., J. Hering, E. Fuchs, P. Barthel, and W. Heim (2014), Genetic barcoding confirms first breeding record of the Yellow Bittern, Ixobrychus sinensis,
(Aves: Pelecaniformes, Ardeidae) in the Western Palearctic, Vert. Zool. 25, 251-260. (pdf)