Carl Nägeli (in 1861) transferred species without alternate branchlets to Antithamnion, Rhodochorton and Acrochaetium.

[11] Then Genevieve Feldmann-Mazoyer in 1941 created genus Aglaothamnion for species having uninucleate cells, zig-zag carpogonial branches and lobed groups of carposporangia, and re-circumscribed Callithamnion.

Aglaothamnion is now sometimes regarded as a synonym of Callithamnion with insufficient evidence for separate evolutionary lines of development.

[2] Callithamnion species are a marine red alga that is monaxial (having only one axis) with free filaments and the thalli are usually small tufts.

[13] In most species are gametophytes and sporophytes are found throughout the year, but are usually only fertile in the late summer and autumn.