Filmy fern

Botanical name: Hymenophyllum sanguinolentum
Synonyms: Mecodium sanguinolentum, Trichomanes sanguinolentum, Hymenophyllum polyanthos var. sanguinolentum, Hymenophyllum sanguinolentum var. lophocarpum, Sphaerocionium sanguinolentum, Hymenophyllum cristulatum, Hymenophyllum lophocarpum
Common name(s): Filmy fern, Piripiri

About:
A common and widespread native filmy fern with dark green, finely divided fronds and a distinctive metallic, blood-like or rusty scent, especially when dried or waterlogged.

Hymenophyllum sanguinolentum forms dense creeping colonies on forest floors, rocks, logs and tree trunks. It is one of New Zealand’s more drought-resistant filmy ferns and is able to survive in comparatively exposed or seasonally dry habitats by curling its fronds tightly during dry conditions.

The dark, often zig-zagged rachis and the crested outer surface of the fertile indusia are particularly useful identification features.

Natural habitat:
Coastal to subalpine forest and shrubland.

Occurs in both closed and open forest, mānuka and kānuka scrub, shaded canyon walls, cliff faces, rock tors, boulder fields, talus slopes, lava, rotten logs, banks and tree trunks.

It may grow terrestrially, on rock or as an epiphyte.

Growing environment:
Shade, Partial Shade, High Humidity, Sheltered & Periodically Dry tolerant. More drought resistant than many other filmy ferns.

Endemic distribution:
Indigenous but not endemic to New Zealand.

Found on Manawatāwhi / Three Kings Islands, the North Island, South Island and Stewart Island/Rakiura.

Also occurs on Rarotonga in the Cook Islands.

Height:
Fronds typically approximately 5–30 cm long, occasionally larger.

Width:
Individual fronds commonly 3–12 cm wide.

Colonies may spread extensively by creeping rhizomes.

Flowering:
Not applicable — fern species reproducing by spores.

Fruiting:
Not applicable — spore producing.

Numerous sori are produced on short terminal branches throughout the distal portions of fertile fronds.

Uses:
• Native fern gardens
• Shaded rock planting
• Moss and log gardens
• Epiphytic displays
• Forest-floor planting
• Native bush restoration
• Humid ferneries
• Specialist drought-tolerant filmy fern planting

Appearance:
Growth habit:
A terrestrial, epiphytic or rock-growing fern forming dense mats from slender, long-creeping rhizomes.

Fronds may overlap closely to form extensive dark green colonies.

Leaves:
Fronds are dark green, membranous and usually three to four times divided.

The lamina is generally ovate, elliptic or elliptic-deltoid and approximately 30–360 mm long by 20–130 mm wide.

The stipe is dark brown to black and narrowly winged for most of its length.

The rachis is also dark and winged throughout, often becoming conspicuously zig-zagged toward the upper part of the frond.

Ultimate segments are oblong, smooth-edged and usually about 0.8–1.5 mm wide.

The frond surface is mostly glabrous, although a few scattered hairs may occur on the basal rachis and costae.

Flowers:
None.

As a fern, Hymenophyllum sanguinolentum does not produce flowers or seeds.

Fruit:
None.

Spores are produced inside numerous sori borne on short branches throughout the pinnae.

Each sorus is enclosed by a two-valved indusium.

The outer surface of the indusium is characteristically crested with several longitudinal ridges, a feature not found in other New Zealand Hymenophyllum species.

The receptacle remains enclosed within the indusial flaps.

Ecology:
Hymenophyllum sanguinolentum is one of the more ecologically versatile New Zealand filmy ferns.

Its fronds can curl tightly into compact masses during dry weather, greatly reducing exposed surface area and allowing the plant to survive temporary desiccation.

When moisture returns, the fronds rehydrate and reopen.

This drought resistance allows the species to occupy sites too exposed for many other filmy ferns, including open scrub, rocky slopes and seasonally dry forest margins.

Its minute spores are dispersed by wind, while the long-creeping rhizomes allow established colonies to spread across suitable surfaces.

Associated habitats:
Kauri forest, podocarp forest, beech forest, broadleaf forest, mānuka scrub, kānuka scrub, shaded cliffs, canyon walls, lava, rock faces, boulders, talus, rotten logs, stumps and tree trunks.

How to grow:
Difficult in cultivation and best left undisturbed in the wild.

Where cultivation is attempted, provide shade or filtered light, high humidity and a cool, well-aerated substrate such as mossy logs, rough bark, rocks or humus-rich woodland soil.

Although more tolerant of drying than many filmy ferns, established plants still perform best where humidity remains relatively high.

Avoid hot exposed sites, prolonged dry winds and excessive root disturbance.

Propagation:
Propagation is by spores.

Spores should be sown on a sterile, consistently moist medium and maintained under high humidity and subdued light.

Vegetative spread occurs naturally through creeping rhizomes, but established wild plants should not be lifted or divided.

Cultural use:
Known by the Māori name piripiri.

The specific epithet sanguinolentum refers to the distinctive smell of the dried fronds, often likened to blood or rusted iron.

Specific traditional uses for this species are not widely documented.

Garden value:
A highly distinctive specialist fern for shaded native plantings.

Its dark green finely divided fronds, black zig-zagged rachis and unusual aromatic character give it strong botanical interest, while its greater tolerance of periodic drying makes it somewhat more adaptable than many other filmy ferns.

It is best suited to mature native gardens, shaded rock faces, mossy logs and naturally humid forest environments where it can slowly develop into dense, intricate colonies.