Tangle Fern

Botanical name: Gleichenia dicarpa
Synonyms: Gleichenia circinnata, Gleichenia dicarpa var. hecistophylla, Gleichenia semi-vestita var. hecistophylla, Gleichenia circinnata var. hecistophylla, Gleichenia dicarpa var. major, Gleichenia hecistophylla, Gleicheniastrum hecistophyllum, Gleicheniastrum hecistophyllum var. majus, Mertensia dicarpa, Platyzoma dicarpum, Calymella dicarpa, Calymella major
Common name(s): Tangle Fern, Swamp Umbrella Fern

About:
A distinctive creeping fern that produces repeatedly forked, umbrella-like fronds and often develops into dense, interwoven colonies. Gleichenia dicarpa is particularly characteristic of New Zealand’s peatlands, pakihi and other acidic wet environments, where its wiry branching fronds can form extensive, almost impenetrable tangles. The tiny rounded ultimate leaf segments have pale to almost white undersides and are distinctly pouched, while fertile segments characteristically contain sori of only two sporangia.

Natural habitat:
Occurs from coastal areas through to subalpine environments, particularly in acidic, nutrient-poor and poorly drained ground. Typical habitats include peat bogs, pakihi, swamp margins, clay pans, seepages and other persistently wet open sites.

In lowland peatlands it can become dominant, producing extensive tangled masses of vegetation from its creeping underground rhizomes.

Growing environment:
Frost, sun, partial shade, wind, wet & poorly draining soil tolerant. Prefers acidic, consistently moist to wet soils and high atmospheric moisture. Unlike many garden ferns, it is naturally adapted to nutrient-poor wetland substrates.

Endemic distribution:
Indigenous but not endemic to New Zealand. Widespread throughout the North Island, South Island, Stewart Island/Rakiura and Chatham Islands. It also occurs naturally in Australia, New Caledonia and parts of Southeast Asia.

Height:
Approximately 10 cm–2 m or more, depending on habitat and the development of its branching fronds.

Width:
Indefinite. Long-creeping rhizomes allow established colonies to spread extensively and form large, dense patches.

Flowering:
Not applicable – fern species.
Gleichenia dicarpa reproduces by spores rather than flowers.

Fruiting:
Not applicable – spore producing.
Fertile fronds develop sori on the undersides of the ultimate segments, with each sorus characteristically containing only two sporangia.

Uses:
• Native wetland restoration
• Peat bog and pakihi restoration
• Acidic wetland planting
• Naturalistic fern gardens
• Erosion and soil-surface protection
• Habitat and biodiversity planting
• Specialist native fern collections
• Revegetation of suitable wet, nutrient-poor sites

Appearance:
Growth habit:
A strongly spreading terrestrial fern arising from slender, extensively creeping rhizomes approximately 1.5–3 mm in diameter. Numerous upright and arching fronds emerge at intervals along the rhizomes and repeatedly fork to produce the characteristic tiered, umbrella-like structure.

Mature colonies become densely intertwined, creating the tangled vegetation responsible for the common name Tangle Fern.

Leaves:
Fronds range enormously in size, from approximately 100 mm to 2 m or more long, and usually develop 1–4 tiers of branches. The lower tiers are commonly more than 150 mm wide and may themselves branch repeatedly.

The smallest ultimate segments are only approximately 0.8–1.5 mm long by 0.8–2 mm wide. They are rounded and blunt rather than sharply pointed, with their margins curved underneath to produce a distinctive pouch-like appearance.

The upper surfaces are generally green and relatively hairless, while the undersides are conspicuously pale or white, although occasionally green. Whitish to rusty-brown scales may occur along the lower midrib.

Flowers:
No flowers are produced. As a fern, Gleichenia dicarpa reproduces through spores rather than flowers and seeds.

Fruit:
No true fruit is produced. Fertile fronds carry rounded sori on the lower surface of the frond segments. Each sorus contains only two sporangia, an important identification feature of the species.

Ecology:
Gleichenia dicarpa is an important structural species of New Zealand peatlands, pakihi and other acidic wet environments. Its long-creeping rhizomes and densely interwoven fronds allow it to occupy large areas, particularly where soils are permanently or seasonally saturated and relatively nutrient poor.

Dense colonies trap organic material amongst the fronds and rhizomes, contributing to the accumulation and stabilisation of wetland substrates. The tangled vegetation also creates sheltered microhabitats for other wetland plants and small animals.

The minute spores are dispersed by wind, enabling colonisation of suitable exposed wet substrates.

Associated habitats:
Peat bogs, pakihi, swamp margins, acidic wetlands, clay pans, seepages, wet heathlands, poorly drained open ground and moist forest or scrub margins.

It is particularly characteristic of open, acidic and nutrient-poor wetlands where it may occur alongside sedges, rushes, mānuka and other specialist bog and pakihi vegetation.

How to grow:
Best suited to specialist wetland or bog gardens where its natural conditions can be closely replicated. Plant in acidic, low-fertility soil that remains consistently moist or poorly drained.

It can grow in open sunny conditions but will also tolerate some shade. Maintaining reliable moisture is particularly important, as established plants should not be allowed to dry out.

Transplanting can be difficult. Gleichenia dicarpa strongly resents disturbance to its fine creeping rhizomes and may fail after apparently successful transplantation. Where establishment is attempted, use plants with as much undisturbed surrounding substrate as possible and maintain high humidity and consistent soil moisture.

Once established in suitable conditions, however, the creeping rhizomes can gradually spread and produce substantial colonies.

Propagation:
Propagation is difficult and generally best attempted from spores or carefully handled rhizome material from cultivated plants.

Spores can be sown onto sterile, acidic and consistently moist fern-growing medium under humid conditions. Development from spores is slow and requires careful control of moisture and contamination.

Division or transplantation of established plants is unreliable because the species resents root and rhizome disturbance.

Cultural use:
No specific traditional Māori uses for Gleichenia dicarpa are widely documented. The species is nevertheless an important component of New Zealand’s indigenous wetland flora and contributes strongly to the distinctive character of peat bog and pakihi landscapes.

Garden value:
A fascinating specialist fern for naturalistic wetland gardens, bog gardens and native plant collections. Its unusual repeatedly forked fronds, tiny pouched leaf segments and dense tangled growth give it a very different appearance from conventional garden ferns.

It is not an ideal general-purpose garden fern because of its specialised moisture and soil requirements and sensitivity to transplantation. However, where acidic, permanently moist conditions can be provided, established colonies can create an exceptionally authentic representation of New Zealand peatland and pakihi vegetation.