Hymenophyllum revolutum (Mini Filmy Fern)

Botanical Name: Hymenophyllum revolutum

Family: Hymenophyllaceae

Discovered By: William Colenso (19th-century botanist)

Common Names: Filmy Fern, Mauku

Overview and Life Cycle

Hymenophyllum revolutum is an exquisite, creeping miniature fern renowned for its breathtakingly delicate fronds. As a true “filmy fern,” its leaves are literally a single cell thick and lack the protective waxy stomata found on standard plants. It is an evergreen perennial that grows slowly, eventually weaving into a dense, turf-like mat that brings a lush, prehistoric aesthetic to any collection.

Origin and Habitat

Endemic strictly to New Zealand, this species thrives in the moist, temperate, and heavily shaded environments of podocarp and broadleaf forests. In the wild, it is primarily an epiphyte or lithophyte, clinging to tree trunks, fallen logs, and damp, moss-covered rocks.

Features and Identification

The defining feature of Hymenophyllum revolutum is its membranous, light-green foliage that appears almost crystalline when backlit. The margins of the leaves are distinctly toothed, and the main stems (rhizomes) are incredibly wiry and thin. It can be distinguished from similar species by these deeply toothed edges and its tendency to grow in creeping, interwoven patches.

Expert Care & Cultivation Guide

Lighting Requirements

Full to partial shade. Because the fronds are unprotected by a waxy cuticle, they cannot tolerate direct sunlight, which will bleach and crisp the leaves within hours. Low, diffused LED lighting is perfect for maintaining healthy growth.

Humidity and Watering

Extreme humidity is non-negotiable. This plant requires an ambient humidity of 80% to 100% at all times, as it absorbs moisture directly through its single-cell leaves. Mist the fronds regularly with distilled or reverse osmosis (RO) water. The root zone must remain evenly moist but never completely waterlogged.

Potting and Mounting

Filmy ferns prefer to be mounted on tree fern fiber, hygrolon, or porous rock rather than traditional potting. If you are growing it in a container, it is critical that the rhizome rests on top of the substrate—it must never be buried inside the pot, as the stems require airflow to prevent rot.

• Recommended Media: Secure the creeping rhizomes lightly over a bed of premium, well-draining mix. We highly recommend using the specialized JB Greens Epiphytic Potting Media, which provides the exact balance of aeration and moisture retention these fragile roots demand.

Nutrient Requirements

Because of their delicate cellular structure, heavy synthetic fertilizers will burn filmy ferns. They require exceptionally low nutrient levels.

• Feeding Routine: Apply a highly diluted, gentle foliar spray once a month during active growth. The organic JB Greens Plant Tonics are ideal for this—simply dilute the tonic to 1/4 strength and mist it directly onto the foliage for safe, optimal nourishment.

Repotting

Handling should be kept to an absolute minimum to avoid damaging the fragile rhizomes. Repot or remount only when the substrate has completely broken down. When transferring, gently lift the entire mat and place it onto the new media, ensuring the stems remain exposed.

Uses in Terrariums & Paludariums

Because of its miniature size and strict demand for high humidity, Hymenophyllum revolutum is a crown jewel for closed environments. It is a flawless candidate for realistic, professional glass terrarium and vivarium displays, whether housed in cylindrical, oval, or square glass enclosures.

• Placement: Mount it on hardscape (wood or stone) in the mid-ground or background where it will receive indirect light and frequent misting.

• Companions: It pairs perfectly with other rare tropical flora that share its love for deep shade and high humidity, making it an excellent companion plant for Sonerila, Labisia, Selaginella, and rare Jewel Orchids.