Hymenophyllum

Hymenophyllum is a genus of ferns in the family Hymenophyllaceae, commonly known as filmy ferns. The name derives from Greek hymen (membrane) and phyllon (leaf), referring to the delicate, membrane-like fronds typical of many species.

The fronds are among the most delicate in the fern group, often translucent and only a single cell layer thick in many parts. They typically have simple to pinnate or bipinnate blades with a short stipe; the leaf tissue is extremely thin, which makes the fronds highly sensitive to desiccation. Sporangia are produced on the undersides of the fronds, usually in linear sori that may be marginal or protected by reflexed edges (false indusia).

Hymenophyllum has a broad tropical and subtropical distribution, with some temperate representatives. Species are mainly epiphytic on tree trunks and branches or lithophytic on rocks, in humid, shaded forests such as cloud and rainforests. They require high ambient humidity, frequent moisture, and protection from direct sun.

Like other ferns, they reproduce by spores produced in the sori. Spores are released and dispersed by wind. Growth is often restricted to microhabitats with constant moisture.

The genus is diverse, comprising numerous species across tropical and subtropical regions. It is one of the defining genera of the family Hymenophyllaceae, which is characterized by thin, membranous fronds.

In cultivation, Hymenophyllum species are grown in terraria, paludariums, or shade houses with high humidity and indirect light. In the wild, many species are sensitive to habitat disturbance and some face threats from deforestation and climate change.