Austral Lady Fern

Botanical name: Diplazium australe
Synonyms: Allantodia australis, Allantodia tenera, Athyrium australe, Athyrium umbrosum subsp. australe, Athyrium umbrosum var. australe, Athyrium brownii, Asplenium australe, Asplenium brownii
Common name(s): Austral Lady Fern, Southern Lady Fern

About:
Diplazium australe is a large, fast-growing terrestrial fern with broad, finely divided dark green fronds. It commonly grows in damp forests, gullies, river flats and disturbed urban habitats. In favourable conditions it can develop a short woody trunk and form an impressive clump, while in cooler areas its fronds may die back during winter and reappear in spring.

Natural habitat:
Occurs in coastal, lowland and montane forest, particularly in alluvial forest, swamp forest, damp gullies and along river flats. It also readily colonises rough pasture, willow stands, drains, urban reserves and other moist disturbed places.

Growing environment:
Prefers moist, fertile, humus-rich soil in full shade or filtered light. It will tolerate full sun when planted in permanently damp ground. Growth is fastest in sheltered, frost-free locations, although established plants can survive cooler conditions by becoming seasonally dormant.

Endemic distribution:
Indigenous but not endemic to New Zealand. Found in the North Island and northern parts of the South Island, though largely absent from dry eastern districts. Its southern limits are near Greymouth in the west and the Marlborough Sounds in the east. It also occurs naturally in eastern Australia, Tasmania and Norfolk Island.

Height:
0.5–2 m, including the fronds

Width:
1–1.8 m

Flowering:
Does not flower. Reproduces by spores.

Fruiting:
Does not produce fruit. Spores are produced on mature fertile fronds.

Uses:
• Shaded native gardens
• Damp woodland planting
• Streamside and wetland-margin restoration
• Large fern displays
• Urban revegetation
• Naturalising beneath established trees

Appearance:
Growth habit:
A terrestrial, tuft-forming fern arising from a short erect rhizome. Older specimens may develop a short, stout woody trunk.

Rhizome:
Short and upright, initially covered with dull dark brown to black scales. It gradually thickens and becomes woody with age.

Fronds:
Broadly triangular, arching fronds measuring approximately 25 cm to 1.2 m long and up to 90 cm wide. They are dark green, thin-textured, hairless and rather brittle, with the blade divided three times into numerous smaller segments.

Stipes:
The frond stalks are 15–80 cm long, deeply grooved and dark or black and scaly near the base. The grooves of the main frond axis remain open where they meet those of the side branches.

Leaflets:
The final segments are oblong, 5–25 mm long, with rounded tips and bluntly toothed or shallowly lobed margins.

Spores:
Elongated sori occur on the undersides of fertile fronds, usually arranged along one side of a vein and occasionally paired back-to-back. This creates a distinctive herringbone-like pattern.

Ecology:
The minute spores are dispersed by wind, allowing the species to colonise damp disturbed ground quickly. Its rapid growth and ability to establish from small rooted pieces can cause it to become locally abundant or weedy, although it also provides cover and humidity for native invertebrates and smaller forest plants.

Associated habitats:
Alluvial forest, swamp forest, lowland rainforest, river margins, damp gullies, willow woodland, rough pasture, shaded drains and urban forest remnants.

How to grow:
Plant in moist, organically enriched soil in shade or filtered light. Keep the root zone consistently damp, particularly during summer. Plants grown in deep shade develop softer, broader fronds, while those in brighter sites require permanently moist soil. Allow adequate space because established plants can grow rapidly and produce a broad crown.

Propagation:
Easily propagated from spores or rooted pieces of rhizome. Fresh spores may be sown onto sterilised, moist growing medium and kept in warm, humid conditions. Established clumps can also be carefully divided.

Cultural use:
No widely documented traditional Māori use is recorded specifically for this species. Its lush form and association with damp forest habitats nevertheless make it a characteristic component of northern New Zealand fern communities.

Garden value:
A bold and attractive fern for damp, shaded gardens. Its large triangular fronds quickly create a lush subtropical appearance and make it particularly effective beneath trees, beside streams or in sheltered woodland plantings. Its vigorous growth means it should be positioned where it has room to spread and can be controlled if necessary.