to the delicate membranous leaf, while the specific epithet, australe, is derived from the Latin australis, meaning southern, in reference to its occurrence in Australia and New Zealand. Notably, New Zealand populations of Hymenophyllum australe were previously divided into a separate species, Hymenophyllum atrovirens, and interpreted as endemic to New Zealand. However, given the absence of distinguishable morphological characters, in addition to recent molecular evidence demonstrating pronounced similarity of the chloroplast DNA sequences of the Australian and New Zealand ferns, Hymenophyllum atrovirens is now considered conspecific with Hymenophyllum australe. Hymenophyllum atrovirens was initially described in 1845 by English botanist William Colenso in his collections from Lake Waikaremoana in 1841. Distribution Hymenophyllum australe is a common fern species of eastern Australia, principally located in the rainforests and fern gullies. It is present in Victoria, from the Otways through to Gippsland and was formally present on the Mornington Peninsula, but recently appears extinct in this area owing to bushfires. It is also found in Tasmania, southern Queensland and New South Wales, in particular the Blue Mountains area. Hymenophyllum australe is also present on both the north and south islands of New Zealand, although there it is less common than in Australia. In Tasmania and New Zealand it has been noted the wings of the fronds are typically smaller and the segments less wrinkled. . Habitat Filmy ferns are typically small in size and limited to wet or misty areas due to the thin, delicate nature of their fronds. Water is rapidly lost under a dry atmosphere and in consequence Hymenophyllum australe will shrivel and collapse as filmy-ferns possess no strengthening tissues in their fronds; being entirely dependent on water pressure to maintain turgidity. As a result, these fragile ferns grow optimally where the air is moist. In New Zealand, Hymenophyllum australe is heavily constrained to growing on rocks, or rarely low on tree trunks, either partially submerged or close to flowing water in shaded habitats. It almost displays a rheophytic habit and is seldom found away from waterways. Conversely in Australia the species grows in a much broader range of habitats, expanding to rock further away from water and additionally as an epiphyte. It is common to wet forests and routinely forms curtains on tree-trunks, logs, wet rocks or on the walls of caves, given there is sufficient light present. In Australia, Hymenophyllum australe is found to display a strong association with