The taxon comprises ~100 species in five currently recognised families. 

Traditional genus-level timetree of extant Pelecaniformes, with the distribution of each family being indicated by the colour-code used throughout this website (Distribution code). The phylogeny of Ardeidae follows Hruska et al. (2023). The divergence times are largely imaginary, except for the divergence times provided by Stiller et al. (2024): (Mesembrinibis + Nipponia) + ((Egretta + Cochlearius) + (Balaeniceps + (Pelecanus + Scopus))). [Chronotaxonomics would split Threskiornithidae into two families and Ardeidae into four families.]

Genus-level classification of extant Ardeidae according to Hruska et al. (2023). 

References

Chesser RT, Yeung CKL, Tao CT, Tian XH, and Lee SH (2010), Molecular phylogeny of the spoonbills (Aves: Threskiornithidae) based on mitochondrial DNA, Zootaxa 66, 53-60. (abstract)

Duan Y, Shao S, Li Y, and Luo X (2018) The complete mitochondrial genome and phylogenetic analysis of White-bellied Heron Ardea insignis (Pelecaniformes: Ardeidae), Mitochondrial DNA Part B 3, 1284-85. (pdf)

Hruska JP, Holmes J, Oliveros C, Shakya S, Lavretsky P, McCracken KG, Sheldon FH, and Moyle RG (2023), Ultraconserved elements resolve the phylogeny and corroborate patterns of molecular rate variation in herons (Aves: Ardeidae), Ornithology 140, e:ukac000. (free pdf)

Huang T, Wang Y, Zhou YL, and Xu Z (2019), Complete mitochondrial genome of Pelcanus crispus and its phylogeny. Mitochondrial DNA Part B 4 (2), 3075-76. (pdf)

Kennedy M, Taylor SA, Nádvorník P, and Spencer HG (2013), The phylogenetic relationships of the extant pelicans inferred from DNA sequence data. Mol. Phylogenet. Evol. 2603, 215-222. (abstract)

Kuhl H, Frankl-Vilches C, Bakker A, Mayr G, Nikolaus G, Boerno ST, Klages S, Timmermann B, and Gahr M (2021), An unbiased molecular approach using 3'UTRs resolves the avian family-tree of life, Mol. Biol. Evol. 38, 108-127. (free pdf)

Kushlan JA, and Hancock JA (2005), The Herons: Ardeidae, Oxford University Press, New York, USA. (link)

Liang WL, Zhu J, and Ren ZM (2019), Complete mitochondrial genome of Ciconia nigra (Ciconiiformes: Ciconiidae), a threatened stork in China. Mitochondrial DNA Part B 4, 2509-2510. (pdf)

Mendales EZ (2023), Ultraconserved elements resolve the phylogeny of a globally distributed genus, Butorides (Aves: Ardeidae), Master Thesis at the San Francisco State University. (pdf)

Päckert M, Hering J, Fuchs E, Barthel F, and Heim W (2014), Genetic barcoding confirms first breeding record of the Yellow Bittern, Ixobrychus sinensis (Aves: Pelecaniformes, Ardeidae) in the Western Palearctic. Vertebr. Zool. 64, 251-260. (pdf)

Prum RO, Berv JS, Dornburg A, Field DJ, Townsend JP, Lemmon EM, and Lemmon AR (2015), A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing, Nature 526, 569-573. (abstract)

Ramirez JL, Miyaki CY, and Del Lama SN (2013), Molecular phylogeny of Threskiornithidae (Aves: Pelecaniformes) based on nuclear and mitochondrial DNA, Genet. Mol. Res. 12, e:3. (pdf)

Sangster G, Kushlan JA, Gregory SMS, and Dickinson EC (2023), Agamiinae, a new family-group name for the Agami Heron Agamia agami (Ardeidae), Avian Syst. 1, 45-49. (pdf)

Zhou X, Lin Q, Fang W, and Chen X (2013), The complete mitochondrial genomes of sixteen ardeid birds revealing the evolutionary process of the gene rearrangements, BMC Genomics 15, 573. (free pdf)