Didymoglossum tahitense (Hymenophyllaceae)

Filmy ferns, or ferns belonging to the family Hymenophyllaceae, are an interesting group of plants.

They are among some of the earliest lineages of ferns, but at the same time, they has a very simple structure, as far as ferns are concerned, because they are usually only one cell thick in most parts of their frond lamina (and thus the appellation ‘filmy fern’).

Being one cell thick, they have also no need for stomata (the microscopic ‘organs’ on the leaves of practically all plants that allow them to transpire), a trait which makes them unique among ferns.

Most filmy ferns live in very wet places such as near waterfalls, or in constantly humid rain forests.

In this latter aspect, filmy ferns are like many mosses and allied plants.

In particular, there a a group of plants called liverworts that are allied to mosses, and the simplest of liverworts are flattish green ‘mats’ known as thalloid liverworts. These liverworts tend to form some sort of a flat plate against their substrate.

Interestingly, there are filmy ferns that do the same, and one such fern is Didymoglossum tahitense.

Being an aficionado of mosses and liverworts (bryophytes in general), small and green plants like filmy ferns pique my interest easily, and especially if they appear flattish and formless.

Thus it was that on a tree in Cape Tribulation, Queensland that I spotted my first Didymoglossum tahitense.

It is one of the strangest filmy fern I have ever seen and has got to be witnessed to be believed, and according to my literature source Ferns of Queensland by S. B. Andrews, this species can also been seen in quite a number of tropical and subtropical regions in Asia, New Guinea, New Caledonia and Polynesia.

More likely, it might be overlooked by most botanists as some algae, liverwort, lichen, some climbing aroid, or possibly even a discoloration of tree bark!

But upon closer inspection, the exquisite often roundish and innervated fronds are unmistakable.