The taxon is restricted to the genus Phaethon (tropicbirds).

Genus-level classification of extant Phaethontidae.

References

Kennedy M, and Spencer HG (2004), Phylogenies of the frigatebirds (Fregatidae) and tropicbirds (Phaethontidae), two divergent groups of the traditional order Pelecaniformes, inferred from mitochondrial DNA sequences, Mol. Phylogenet. Evol. 31, 31-38. (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-level tree of life, Mol. Biol. Evol. 38, 108-127. (free pdf)