BOLBITIS DIFFORMIS

This tiny fern is sold under various trade names, e.g. e.g. "mini Bolbitis", "Davallia spec." and "Bolbitis Davallia spec.". It has nothing to do with the ferns of the genus Davallia but is a dwarf form of the widely spread and extremely variable tropical Asian fern Bolbitis heteroclita. It was originally described as a species of its own (Edanyoa difformis), originates from the Philippine island Negros and has been in horticultural cultivation for a long time. It has only recently been discovered as aquarium plant, though.
Diverse small ferns of the Hymenophyllaceae family are sold under the name "mini Bolbitis", though, and it cannot be said exactly which species they belong to and whether they are suitable for aquarium cultivation.