Antoithamnion hubbsii is a red alga, which was described from the Gulf of California in 1962. It is presumed to be native to the Pacific, most likely to the Northwest Pacific. It has been reported under the names A, nipponicum* and A. pectinatum..It has been collected north to Half Moon Bay California, and from Japan, Korea, and China, and from New Zealand, Australia, and eastern South Africa. It has been reported as an introduced species on the East Coast, Europe, and the Azores. It's a small (150-300 mm) seaweed which grows on rocks and other algae in low intertidal and shallow subtidal zones. The fronds have symmetrical branches and branchlets, giving a delicate appearance, It was first reported on the East Coast on Millstone Point, Long Island Sound Connecticut in 1985t. On the East Coast, it occurs from North Carolina to Cape Cod, and possibly Maine. In Europe, it has been reported from Norway, Atlantic France and Spain, Mediterranean France, Italy, and Turkey, and also the Azores. Possible vectors includde ballast water and hull fouling. This alga is is easily overlooked, and no impacts are reported.
Currently, the AlgaeBase website (Guiry and Guiry 2024) uses the name A. nipponicum, while Mathieson and Dawes (2017) uses A. nipponicum in their seaweed listings. Identification of these seaweeds is challenging, and requires molecular identification.