Prickly Rasp Fern

Botanical name: Doodia aspera
Synonyms: Woodwardia aspera, Blechnum neohollandicum
Common name(s): Prickly Rasp Fern

About:
Prickly Rasp Fern is a vigorous, creeping terrestrial fern with harsh-textured fronds and attractive pink to reddish new growth. It spreads by long rhizomes that can form dense colonies or carpets beneath trees and across exposed ground. Although indigenous to New Zealand, genuine wild populations are now believed to be extinct here, and many plants in cultivation are of Australian origin or are hybrids with Doodia australis.

Natural habitat:
Formerly recorded from coastal scrub and inland forest in Northland, including sites beneath rawirinui or kānuka forest. Elsewhere in its natural range it occurs in rainforest margins, tall open forest, damp gullies and dry forest on sandy, gravelly or rocky soils.

Growing environment:
Prefers light shade to filtered sun in moist, acidic, free-draining soil with some organic matter. It tolerates exposed clay soils and brief dry periods once established but is sensitive to cold and may slow down or die back during winter, even in relatively mild northern districts.

Endemic distribution:
Indigenous but not endemic to New Zealand. It is widespread in eastern Australia and also occurs on Norfolk Island. In New Zealand it was historically recorded from Northland, but genuine wild populations are now thought to be extinct.

Height:
20–45 cm, occasionally taller

Width:
Individual colonies may spread 1 m or more through creeping rhizomes.

Flowering:
Not applicable—spore-producing fern

Fruiting:
Not applicable—spore-producing fern

Uses:
• Woodland groundcover
• Shaded banks and slopes
• Fern gardens
• Erosion control
• Revegetation beneath established trees
• Decorative foliage planting

Appearance:
Growth habit:
A terrestrial fern forming scattered clumps or dense spreading colonies. Long creeping rhizomes extend above and below the soil, rooting and producing fronds at intervals.

Rhizome:
The rhizome is up to about 10 mm thick and may spread for more than 1 m. It is covered with persistent black scales and old dark stipe bases, with the growing tips often turning slightly upward.

Stipes:
Stipes are generally 10–30 cm long, dark and rough, and clothed with black to blackish-brown scales. Fine hairs may also be present.

Fronds:
Fronds are 12–40 cm long and 2.5–10 cm wide, narrowly elliptic to elliptic and pinnate. Young fronds emerge pink, reddish-pink or pinkish-green before maturing to dark green. Under poor conditions they may become yellow-green.

Pinnae:
There are usually 15–38 pairs of narrow pinnae. Most are fused directly to the rachis, although the lowest pair may occasionally be shortly stalked. The margins are toothed, and the frond surface is distinctly rough and rasp-like.

Spores:
Rounded to kidney-shaped sori occur in one or two rows on either side of the pinna midrib. Each sorus is covered by a small reniform indusium, and the mature spores are dispersed by wind.

Ecology:
Prickly Rasp Fern spreads vegetatively through its extensive rhizome system and can quickly occupy open ground beneath taller vegetation. Its dense growth protects the soil surface, traps litter and provides cover for small invertebrates. Wind-dispersed spores allow it to colonise suitable disturbed habitats when fertile plants are present.

Associated habitats:
Coastal scrub, kānuka forest, rainforest margins, tall open forest, damp gullies, clay banks, rocky slopes and shaded woodland floors.

How to grow:
Plant in partial shade or filtered sun in moist but well-drained soil. Water regularly during establishment and provide shelter from heavy frost. Once established, it can spread rapidly and may be useful beneath tall trees or on difficult clay banks. Its rhizomes should be contained where unrestricted spread is not wanted.

Propagation:
Easily propagated from fresh spores or rooted sections of rhizome. Rhizome divisions establish quickly when kept moist and shaded. Care should be taken to verify the identity and provenance of cultivated plants because Australian material and sterile hybrids with Doodia australis are also present in New Zealand collections.

Cultural use:
No specific traditional Māori uses are widely recorded. The species is nevertheless of considerable conservation interest because authentic New Zealand populations may no longer survive in the wild.

Garden value:
An attractive and useful groundcover fern with vivid reddish new fronds and a bold, rough-textured appearance. It performs well beneath trees, on banks and in naturalistic fern gardens, although its frost sensitivity and vigorous spreading habit should be considered before planting.