Octodiceras fontanum is, according to R. A. Pursell (1987)1, a synonym of Fissidens fontanus. This species belongs to a group of a few closely related, very similar species. Depending on the author, this group is treated as a distinct genus (Octodiceras) separate from Fissidens or placed as the subgenus Octodiceras within the genus Fissidens.
In botanical literature and in the aquarium hobby, the name Octodiceras fontanum is still frequently used. Various variants of the species Fissidens fontanus are apparently cultivated as aquarium mosses, and for this reason it is often believed that F. fontanus and Octodiceras fontanum are names for two different moss species. However, the two names clearly refer to the same species, because they relate to the same type.
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