The red algal genus Mychodea Hook.f. & Harv. is not only Australia’s largest wholly endemic macroalgal genus, it and the family Mychodeaceae (of which it is the sole member) appear to be the largest completely endemic algal genus and family from any continental landmass in the world. Kraft’s 1978 morpho-taxonomic monograph credited Mychodea with 11 species varyingly distributed between Geraldton, Western Australia, south and eastward across the coasts of South Australia, Victoria and Tasmania, and northwards into southern New South Wales. Dismissed or discounted was every former extra-Australian attribution of the genus. In the over 40 years since completion of the research, further explorations of marine habitats in Australia have uncovered additional species, and the application of molecular-assisted taxonomic and phylogenetic methodologies has now allowed a substantial refinement of Mychodea systematics. We here document 19 Mychodea species, for 16 of which we have molecular data that support inferences of probable species relationships. To the 11 species treated by Kraft we now add 4 that are recently discovered, resurrect 2 that were synonymised with a third species in his 1978 work, and treat 2 species-level Western Australian entities that remain unnamed for lack of sufficient reproductive material. Mychodea is characterised by elaborate vegetative structures and some of the most complex fertilisation, diploidisation and embryogenesis processes of any red alga, which we detail and illustrate. Distinguishing features of the individual species are highlighted, some of which are particularly unusual.