Fork Fern
Tmesipteris tannensis
Tmesipteris tannensis , commonly known as the Fork Fern, is a primitive and evolutionarily ancient fern ally endemic to New Zealand. This curious plant belongs to the Psilotaceae family, a lineage so old it lacks true roots, instead relying on a creeping rhizome and microscopic fungi to absorb nutrients. Tmesipteris tannensis is a true specialist of the vertical rainforest, almost always found growing epiphytically on the fibrous, moisture-holding trunks of tree ferns like the Silver Fern ( Cyathea dealbata ) or Whekī ( Dicksonia squarrosa ). With its pendulous, unbranched stems and glossy, leathery leaves, it adds a layer of intricate detail to the forest understory. Classified as "Not Threatened," it is a common but often overlooked resident of New Zealand's wet forests, representing a living link to the prehistoric world. While extremely difficult to cultivate, it is a plant of great significance to botanists and a symbol of the complex vertical biodiversity of Aotearoa's native ngāhere (forests).
Plant Description
Fork Fern is characterized by its pendulous or occasionally suberect aerial stems, which typically range from 5 to 80 cm in length. These stems are usually unbranched, though they may occasionally fork once. Lacking true roots, the plant is anchored by a creeping, branching rhizome that is densely covered in fine rhizoids.
The leaves (technically microphylls) are spirally arranged along the stems and are quite brittle. They are narrowly ovate to elliptic in shape, measuring 7-28 mm long and 2-8 mm wide. Each leaf is glossy dark green above and dull green beneath, typically ending in a small, sharp point (mucro). The reproductive structures, known as synangia, are biconic (diamond-shaped) and about 3-8 mm long. These are fused in pairs and located on the upper surface at the base of specialized forked fertile leaves. When mature, these structures release fine spores into the forest air.
Quick Facts
Plant Specifications
| Scientific Name | Tmesipteris tannensis |
|---|---|
| Family | Psilotaceae |
| Height | 5-80 cm (Pendent) |
| Growth Form | Pendulous epiphytic fern ally |
| Foliage | Small, glossy, brittle lance-shaped leaves |
| Reproduction | Spore-bearing synangia; Summer/Autumn |
| Light | Deep to partial shade |
| Soil | Not applicable (usually grows on tree fern trunks) |
| Hardiness | Hardy; requires high humidity and shelter |
| Water Needs | High; requires constant moisture/humidity |
| Spread | Individual stems; often clustered |
| Frost Tolerance | Moderate (protected by forest canopy) |
| Salt Tolerance | Moderate |
| Growth Rate | Very Slow |
| Lifespan | Perennial |
Climate Best Suited to
Fork Fern is a plant of New Zealand's high-humidity, high-rainfall forest zones. It thrives in the temperate and subtropical climates of both the North and South Islands. It requires a stable environment where the air never becomes too dry. While it can handle the cool temperatures of Stewart and the Auckland Islands, its survival is entirely dependent on the presence of its tree fern hosts, which provide the necessary microclimate and moisture.
Regional Suitability
| Whangārei | Ideal |
| Auckland | Ideal |
| Hamilton | Ideal |
| Rotorua | Ideal |
| Tauranga | Ideal |
| Gisborne | Suitable |
| New Plymouth | Ideal |
| Whanganui | Ideal |
| Palmerston North | Ideal |
| Napier | Suitable (needs high shade) |
| Wellington | Ideal |
| Nelson | Ideal |
| Christchurch | Suitable (requires humidity) |
| Dunedin | Ideal |
| Invercargill | Ideal |
| City | Climate Suitability |
|---|
Plant Habitat
Tmesipteris tannensis is found throughout New Zealand, from sea level up to subalpine forest zones (approx. 1100m). Its habitat is almost exclusively vertical: it is an obligate epiphyte that perches on the trunks of tree ferns. Its favorite hosts are Cyathea and Dicksonia species, whose fibrous "skirt" of old fronds and aerial roots provides a constant reservoir of moisture and nutrients. Occasionally, it can be found growing terrestrially on mossy rock faces, peat mounds, or in the deep leaf litter of Kauri forests, but these sites always mimic the high-organic, humid conditions of a tree fern trunk. It is a key indicator species for mature, healthy rainforest ecosystems.
Plant Conservation
Fork Fern is currently classified as "Not Threatened." It remains common and widespread, reflecting the relative abundance of its tree fern hosts in protected forest areas. However, because it is an obligate epiphyte, its long-term survival is inextricably linked to the health of New Zealand's forests. The loss of primary forest through logging or land clearance directly removes the habitat this species requires. Furthermore, the drying of forest edges due to fragmentation can lead to a drop in humidity that kills the sensitive aerial stems. Conservation focuses on the preservation of intact forest blocks and the protection of tree ferns from illegal harvesting.
Growing Requirements
Substrate Requirements
Does not grow in traditional soil. It requires a moisture-holding, fibrous substrate. In a garden setting, it must be grown on a tree fern trunk or a moss-lined vertical surface.
- Tree fern trunk (host)
- High organic matter (humus)
- Constant moisture availability
Light Requirements
Demands partial to deep shade. It is a specialist of the forest understory and will quickly scorch and die if exposed to direct, drying sunlight.
- Deep to partial shade
- Cool, sheltered position
- No direct midday sun
Water Requirements
Requires very high humidity and consistent moisture. It has no true roots to seek water deep underground, so it relies entirely on the dampness of its host surface and the air.
- Constant high humidity
- Frequent misting in dry spells
- Host surface must stay damp
Planting Guide
Best Planting Practices
Cultivation of Fork Fern is extremely difficult and is generally not recommended for the average home gardener. The best way to "grow" this plant is to preserve the tree ferns already present in a forest-style garden. If you must attempt planting, it should involve transplanting a section of tree fern trunk that already hosts the fern. Ensure the host is placed in a deep-shade, high-humidity spot - ideally near a pond or a damp gully. It cannot be "planted" into the ground. It is strongly advised never to remove this species from the wild, as the chances of successful establishment in a garden are very low.
Ecological Role
Environmental Benefits
Fork Fern is a vital contributor to the vertical complexity of New Zealand's forests. By inhabiting tree fern trunks, it creates additional layers of habitat for specialized forest invertebrates and microorganisms. It participates in the intricate cycling of nutrients within the forest canopy and serves as a living museum of primitive plant evolution, maintaining genetic diversity that dates back millions of years.
Uses & Significance
Garden Significance
Valued for its botanical interest and prehistoric appearance:
- Ultimate indicator of a healthy native forest garden
- Exceptional textural interest on tree fern trunks
- Fascinating educational plant for primitive botany
- Symbol of vertical rainforest biodiversity
Ecological Value
Supports specialized forest-dwelling invertebrates and primitive microbes.
Cultural Significance
Traditional Uses and Values
Fork Ferns are recognized as part of the ancient fabric of the New Zealand ngāhere. While specific traditional records are rare, they are respected as a taonga of the vertical forest. Today, they are symbols of the deep time and complex interdependencies of our native ecosystems, representing a lineage of plants that predates the arrival of flowering species.
Landscaping Uses
Garden Design Applications
In high-end native forest designs, Tmesipteris tannensis is used to create a sense of deep, ancient lushness. It is never a stand-alone feature but part of a multi-layered ecosystem. Seeing Fork Ferns hanging from the trunks of established Silver Ferns immediately signals to the viewer that they are in a mature, well-curated native environment. It is the perfect detail plant for a shaded "gully" or a sheltered backyard bush walk where the goal is complete ecological immersion.
Seasonal Care
Spring
Ensure high humidity as air warms; monitor host tree health.
Summer
Frequent misting required; protect from hot, dry winds; enjoy the glossy foliage.
Autumn
Spore release period; ensure the host trunk is clear of aggressive exotic weeds.
Winter
Fully hardy if sheltered; ensure the forest canopy remains intact for thermal protection.
Pruning
Pruning Techniques
Fork Fern requires absolutely no pruning. The only maintenance recommended is the removal of any competing exotic weeds or climbing plants from the host tree fern trunk that might smother the Fork Fern. Dead aerial stems will eventually fall away naturally and should not be forcibly removed to avoid damaging the delicate creeping rhizome.
How to Grow Fork Fern
Success depends on recreating its natural habitat. Choose a shaded, humid corner and a healthy tree fern or rough-barked host where moisture is retained but not stagnant. Keep air humidity high with regular misting, especially through summer, and avoid drying winds. A living mulch of mosses and small ferns on the host trunk helps stabilize moisture and provides the micro-fungal community the plant relies on.
From Spores
Propagation from spores is theoretically possible but extremely difficult and slow. Spores are released in late summer and must land on a suitable host surface (like damp tree fern bark) that is already inhabited by the correct mycorrhizal fungi. Without this fungal partnership, the plant cannot establish. This is rarely achieved outside of its natural forest environment.
Natural Spread
The best way to increase the presence of Fork Fern in a suitable garden is to encourage the health of the host tree ferns. If conditions are right (cool, moist, and shaded), the fern will spread naturally through the slow expansion of its creeping rhizomes and the occasional successful germination of wind-blown spores.
Troubleshooting Common Issues
The single biggest problem is drying out. If the aerial stems begin to turn yellow and go limp, the air or the host surface is too dry. Increase misting and shade. If the plant disappears entirely, it is usually a sign that the forest microclimate has been compromised (e.g., through the removal of surrounding trees). It is not affected by common garden pests but can be smothered by invasive climbing plants.
Pests & Diseases
Remarkably resistant to typical garden pests. Its primary "disease" is environmental stress from low humidity. It is an extremely "clean" plant when growing in its preferred forest setting.
Bonus Tip
If you have a shaded area with tree ferns, use an automatic misting system during the height of summer. This not only keeps your tree ferns healthy but provides the perfect environment for Fork Ferns to establish and thrive naturally.
