Swamp Shield Fern

Botanical name: Cyclosorus interruptus
Synonyms: Pteris interrupta, Thelypteris interrupta, Nephrodium propinquum, Nephrodium inaequilaterum, Nephrodium unitum, Cyclosorus gongyloides, Dryopteris gongylodes var. glabra, Dryopteris gongylodes

Common name(s): Swamp Shield Fern, Hottentot Fern

About:
Cyclosorus interruptus is a robust wetland fern naturally occurring in the warmer parts of New Zealand and throughout much of the tropical and subtropical world. It forms spreading colonies from creeping rhizomes and produces attractive leathery olive-green fronds. In New Zealand it is primarily associated with geothermal wetlands, swamps and frost-free lowland habitats, where it plays an important role in wetland ecosystems.

Natural habitat:
Freshwater swamps, geothermal wetlands, raupō wetlands, marshes, stream margins and permanently damp lowland sites.

Growing environment:
Prefers full sun to partial shade in permanently moist or waterlogged soils. Thrives in frost-free areas with consistently high soil moisture.

Endemic distribution:
Indigenous to New Zealand, occurring naturally from Te Paki to Kawhia Harbour, Bay of Plenty, Rotorua, Taupō and East Cape. Also widespread through Australia, Asia, the Pacific, Africa and the Americas.

Height:
50–100 cm

Width:
Spreads indefinitely by creeping rhizomes.

Flowering:
None – ferns do not flower.

Fruiting:
Spores may be produced throughout the year.

Uses:
• Wetland restoration
• Pond and stream margins
• Geothermal landscape planting
• Rain gardens
• Native fern collections
• Habitat restoration

Appearance:
Growth habit:
A creeping fern forming extensive colonies from underground rhizomes.

Leaves:
Harsh, leathery olive-green fronds up to 80 cm long. Fronds arise on slender dark stalks that are almost black near the base. Each frond carries 9–15 pairs of leaflets, with the lower pair noticeably larger and sickle-shaped.

Flowers:
None. Reproduces by spores.

Fruit:
Spores develop in closely packed sori positioned nearer the midrib than the leaflet margins and may be present throughout the year.

Ecology:
An important fern of warm wetlands where it provides shelter for wetland fauna and contributes to soil stabilisation. Minute spores are dispersed by wind, allowing new colonies to establish where suitable damp conditions exist.

Associated habitats:
Raupō swamps, geothermal wetlands, freshwater marshes, sedgelands, stream margins and lowland wet forest.

How to grow:
Grow in permanently moist to waterlogged soil in full sun or light shade. It performs best in frost-free districts and should never be allowed to dry out completely.

Propagation:
Very easily propagated by division of creeping rhizomes or by sowing fresh spores. Divisions establish quickly when kept consistently wet.

Cultural use:
Although there are no widely recorded traditional Māori uses in New Zealand, the species has been used medicinally in several tropical countries.

Garden value:
An outstanding fern for ponds, wetlands and bog gardens where few other native ferns thrive. Its lush olive-green foliage provides year-round texture while its vigorous spreading habit makes it valuable for stabilising wet soils and naturalising damp landscapes.