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 placement of Oroanassa magnifica (resurrected from Gorsachius magnificus) is based on Zhou et al. (2016). 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 the Botaurinae and Ardeinae suggests that it evolved and 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)
Tu, F., S. Tang, C. Yan, and X. Huang (2017), Complete mitogenome of Intermediate Egret Ardea intermedia (Ciconiiformes: Ardeidae), Mitochondrial
DNA, Part B 4(2), 2509-2510. DOI 10.1080/23802359.2017.1361352. (pdf)
Zhou, X., C. Yao, Q. Lin, W. Fang, and X. Chen (2016), Complete mitochondrial genomes render the Night Heron genus Gorsachius non-monophyletic,
J. Ornithol. 157: 505-513. DOI 10.1007/s10336-015-1297-z. (abstract)