Adder's Tongue
Ophioglossum coriaceum
Ophioglossum coriaceum , commonly known as Adder's Tongue, is a unique and evolutionarily primitive fern endemic to New Zealand and several other regions in the Southern Hemisphere. This curious little plant is quite unlike the lush, feathery ferns most are familiar with. Instead, it features a single, leathery leaf (the sterile lamina) and a separate, upright spore-bearing spike (the sporophore) that rises above it, resembling the tongue of a serpent. Found in a vast range of habitats - from damp coastal dunes to high-altitude alpine basins - it is a tough and adaptable survivor. While small and often overlooked, the Adder's Tongue is a master of colonizing open, disturbed ground and damp, low-nutrient soils. Classified as "Not Threatened," it represents a living link to the ancient history of plant life on Earth and is a fascinating addition to specialized rock gardens or native collections.
Plant Description
Ophioglossum coriaceum is a small terrestrial fern that typically grows to between 5 and 20 cm in height, though it can reach 25 cm in very wet conditions. It grows from an erect, cylindrical rhizome with fleshy, orange-brown roots. The fern usually produces only one or two fronds at a time, though mature colonies can form extensive mats through vegetative budding from the roots.
Each frond is divided into two distinct parts. The sterile, leafy portion (lamina) is fleshy, leathery, and a bright green to yellow-green colour. It is typically elliptic or ovate in shape, measuring 8-30 mm long. The fertile portion (the sporophore) is an upright, narrow spike that is usually much longer than the leaf, reaching up to 10 cm or more. This spike bears two rows of 3-17 pairs of deeply embedded sporangia (spore cases) that release fine yellow spores when mature. The species name "coriaceum" refers to the leathery, tough quality of the sterile leaf, which helps the plant withstand exposure.
Quick Facts
Plant Specifications
| Scientific Name | Ophioglossum coriaceum |
|---|---|
| Family | Ophioglossaceae |
| Height | 5-25 cm |
| Growth Form | Small terrestrial fern |
| Foliage | Single leathery, oval green leaf per frond |
| Spores | Upright fertile spike; Summer/Autumn |
| Light | Full sun to partial shade |
| Soil | Moist, fertile, well-drained to boggy |
| Hardiness | Very hardy; tolerates alpine frost and wind |
| Water Needs | Moderate to high; likes consistent moisture |
| Spread | Forms colonies 10-30 cm across |
| Frost Tolerance | Very High |
| Salt Tolerance | Moderate |
| Growth Rate | Slow |
| Lifespan | Perennial |
Climate Best Suited to
Adder's Tongue is incredibly versatile and can be found in almost every New Zealand climate zone. It is equally at home in the humid, warm North Island and the cold, alpine regions of the South Island. It thrives in areas with reliable moisture, whether from high rainfall or groundwater seepages. It is very hardy to typical New Zealand winter frosts and can tolerate high-altitude snow cover.
Regional Suitability
| Whangārei | Suitable |
| Auckland | Suitable |
| Hamilton | Suitable |
| Rotorua | Ideal |
| Tauranga | Suitable |
| Gisborne | Suitable |
| New Plymouth | Ideal |
| Whanganui | Ideal |
| Palmerston North | Ideal |
| Napier | Suitable (needs moisture) |
| Wellington | Ideal |
| Nelson | Ideal |
| Christchurch | Ideal |
| Dunedin | Ideal |
| Invercargill | Ideal |
| City | Climate Suitability |
|---|
Plant Habitat
The habitat of Ophioglossum coriaceum is remarkably diverse. It is found throughout New Zealand, from the Kermadec Islands to the subantarctic. It occurs in lowland, montane, and subalpine zones. Its preferred environments include damp grasslands, forest clearings, the margins of lakes and rivers, and peat bogs. It is also found in more extreme sites such as stable sand dunes, rocky outcrops, and even around geothermal vents where soil temperatures are elevated. It is a specialist of open ground where competition from taller plants is limited by either extreme conditions or recent disturbance.
Plant Conservation
Adder's Tongue is currently classified as "Not Threatened." It remains common and widespread, although its small size and tendency to go dormant in dry periods mean it is often under-recorded in botanical surveys. While the species as a whole is secure, localized populations can be threatened by the invasion of aggressive exotic grasses or the drainage of the damp wetland areas it favors. Protecting small, damp open spaces and preventing the complete overgrowth of rock faces by exotic weeds are important for maintaining its presence in more developed landscapes.
Growing Requirements
Soil Requirements
Prefers moist, fertile soil but is surprisingly adaptable. It performs best in a loamy or peaty mix that stays consistently damp but has reasonable air movement.
- Moist, fertile loam
- Peaty or organic-rich soil
- Tolerates stony or rocky pockets
Light Requirements
Thrives in full sun to partial shade. In its natural open habitats, it benefits from high light levels, but in a garden setting, a semi-shaded spot will help maintain soil moisture.
- Full sun to semi-shade
- Appreciates high light
- Shelter from intense dry heat
Water Requirements
Requires consistent moisture to thrive. It does not tolerate prolonged drying out of the root zone. If the soil becomes too dry, the plant will often go dormant until moisture returns.
- Regular watering essential
- Likes consistently damp soil
- Avoid waterlogging in pots
Planting Guide
Best Planting Practices
Plant in autumn or spring when the soil is naturally moist. Choose a site that is cool and won't dry out in the summer sun. Dig a small hole and enrich with some leaf mould or peat. Carefully place the plant, ensuring the fleshy roots are spread out gently. Firm the soil down and water in thoroughly. Because this fern is small and can be easily overwhelmed, it is best planted in a dedicated rockery pocket or at the edge of a pond where it won't be smothered by larger plants. Providing a light mulch of fine bark or moss will help retain the surface moisture it needs.
Ecological Role
Environmental Benefits
Adder's Tongue is a fascinating part of New Zealand's primitive biodiversity. Its spores provide food for tiny soil invertebrates, and its colonies help to stabilize damp, open ground. It is an important part of the complex web of life in alpine and wetland edges, where it represents one of the most ancient lineages of vascular plants still surviving today.
Uses & Significance
Garden Uses
A unique and educational choice for the specialist gardener:
- Intriguing feature in rock or scree gardens
- Excellent for small pots or alpine troughs
- Great addition to moist native grassland plantings
- Educational plant for demonstrating primitive botany
Ecological Value
Protects soil moisture and adds to the diversity of specialized open-ground habitats.
Cultural Significance
Traditional Uses and Values
The Adder's Tongue fern is part of the rich tapestry of New Zealand's native flora. While specific traditional medicinal uses are not as prominent as for some other ferns, its unique form was certainly noted. Today, it is valued by botanists and indigenous ecologists as a "taonga" of New Zealand's open wetlands and alpine edges, representing the ancient botanical heritage of the land.
Landscaping Uses
Garden Design Applications
In landscape design, Ophioglossum coriaceum is used for its incredible detail and "primitive" aesthetic. It is a perfect choice for a "fernery" or a shaded rock garden where its unique sporophores can be appreciated up close. It is best used in small-scale designs where its form won't be lost. Pairing it with other low-growing natives like Mazus radicans or Leptinella creates a beautiful, detailed groundcover tapestry. It is also an excellent choice for a terrarium or an indoor ferneries in a cool spot.
Seasonal Care
Spring
Check for the emergence of new fronds; apply a very light organic feed.
Summer
Ensure consistent watering; watch for the development of the spore spike.
Autumn
Spore release period; optimal time for division if the soil is moist.
Winter
Plant may go semi-dormant; fully hardy; ensure the site stays damp.
Pruning
Pruning Techniques
This fern requires almost no pruning. The only maintenance needed is the removal of any brown or damaged fronds in early spring to make way for new growth. This should be done carefully with small snips to avoid damaging the delicate rhizome. Do not prune the fertile spike until it has completely finished releasing its spores and turned brown.
How to Grow Adder's Tongue
Aim for a cool, consistently damp site with dappled light and free-draining, humus-rich soil. This species dislikes hot, dry conditions, so avoid exposed, baking positions. A thin layer of leaf litter or fine bark helps keep the soil evenly moist without smothering the crown. Keep nearby weeds in check; the small fronds are easily shaded out by faster growers.
From Seed (Spores)
Propagation from spores is possible but notoriously slow and difficult. Collect the yellow spores in late summer. Sow them onto a sterilized, moist, organic-rich medium. Place the tray in a humid, bright (but not direct sun) spot. Germination can take many months, and the young prothalli are very delicate. This method is generally only attempted by specialist growers.
From Division
The most practical way to increase your stock is through division. Large, established colonies can be carefully lifted in autumn or spring. Ensure each division has a portion of the rhizome and several healthy roots. Replant immediately in a moist, shaded spot. Because the roots are fleshy and fragile, they must be handled with extreme care to prevent breakage.
Troubleshooting Common Issues
The most common cause of failure is drying out. If the plant disappears in summer, it is likely dormant due to drought - increase watering. Slugs and snails are the primary pests, as they love the succulent, fleshy fronds. Ensure you have a non-toxic slug management system in place. High humidity and poor air movement in very warm districts can lead to minor fungal issues.
Pests & Diseases
Vulnerable to slugs and snails who can quickly consume the entire frond. Generally free of major plant diseases if its moisture and light needs are met. Its small size means it can be easily smothered by more vigorous weeds or garden plants.
Bonus Tip
Adder's Tongue is a great "indicator plant." If it is thriving in your garden, it means you have achieved a perfect balance of moisture, light, and soil health. It is a reward for the patient and observant gardener.
