I admit I am a little confused about a fern that is traded as the 'mini Bolbitis', in reference to that genus of ferns. It is in fact Trichomanes auriculatum, a species belonging to quite a different subclade of ferns, and a relative of Crepidomanes minuta - a popular terrarium fern, itself sometimes mis-sold as an underwater aquarium plant. Sometimes it is actually traded as Crepidomanes auriculatum, although consensus has it that the species belongs instead to the allied genus Trichomanes. In any case, the circumscription of the related genera is unclear, and both belong to the fern subclade named the filmy ferns or bristle ferns, that are common in tropical rainforest.
C. auriculatum is a widespread plant with a distribution from Himalayan South Asia, to the Japanese archipelago, and down to New Guinea; the latter large island has a mainly Australian fauna, and was formerly connected by land to the mainland of Australia; but also possesses a flora that has more connections to tropical Asia. This is because plants, although they cannot swim or fly, are better able to cross the straits than do those animals which are unable to fly, including for example the freshwater fish and crayfish of New Guinea, which belong of course to Australian rather than Asian types.
Supposedly C. auriculatum is not a true aquatic fern, but it ably tolerates submergence, at least temporarily, if the level of dissolved carbon dioxide is sufficiently high. In nature it is a climbing epiphyte, and it is often associated with tree stumps when it is encountered, in the forests within the wet tropical biome. In the aquarium it has an unstable reputation, as some people report the species dies quickly, whereas other anecdotes report success. At least primarily this is a terrestrial fern.
Whatever it's taxonomy or natural growth habit, the so-called mini Bolbitis requires low to moderate lighting, and when it is grown emersed - as in nature - it requires good air humidity. For this reason T. auriculatum is an excellent plant to include in warm, humid aquaterrariums - in the terrestrial part - or in rainforest themed setups, as intended for fauna such as mantellas and dart frogs.
All the same information might be held to apply to Trichomanes intramarginale, which is often traded as 'C. malabaricum'. This is a fern from the tropics of South India and the island of Sri Lanka. Again this is a filmy fern from warm and humid environments, that I can find traded as an aquarium plant, but surrounded by no consensus of reputation, as regards its ease or otherwise of care. Perhaps it is best to regard the entire clade as poorly to wholly unsuited to life underwater, which forces us to ask, how they fare so long in aquaria at all.
Because of their delicate and unusual fronds, filmy ferns are essentially dependent upon the presence of high moisture in their environment - although to my knowledge, none of them are really aquatic plants. It is only when the environment is very humid, that filmy ferns may grow upon rocks or wood; the filmy coats of their fronds, are the primary surface through which they obtain their necessary water.
The ‘resemblance’ of some filmy ferns to the mosses and liverworts, is not merely superficial, and involves a strong dependence on environmental moisture, and a secondary reduction of their epidermis and roots; these are traits unique to the filmy ferns, although dwarfism is encountered in other epiphytic ferns, and in some other epiphytic plants, such as the orchid family.
