Kermadec Rasp Fern

Botanical name: Doodia milnei
Synonyms: Doodia milnei var. milnei, Doodia caudata var. milnei, Doodia media var. milnei, Blechnum kermadecense
Common name(s): Kermadec Rasp Fern, Milne’s Rasp Fern

About:
Kermadec Rasp Fern is a distinctive fern endemic to the Kermadec Islands. It forms broad, bright green fronds from an upright rhizome that may eventually develop into a short trunk-like caudex. Unlike many related rasp ferns, its emerging fronds are always green and never pink or reddish. It is common in the warmer, drier forests of Raoul Island but remains naturally restricted to a very small island range.

Natural habitat:
Occurs in coastal and lowland island forest, particularly beneath Kermadec pōhutukawa. It grows among rocks, in deep leaf litter, on dry forest floors and across shaded cliff faces. On Macauley Island it has also been recorded beneath sparse Kermadec ngaio vegetation.

Growing environment:
Prefers warm, frost-free conditions in full sun or light shade. It grows best in dry to moderately moist, free-draining soil and does not tolerate prolonged waterlogging or excessive moisture. It is cold sensitive and is best protected from low temperatures.

Endemic distribution:
Endemic to New Zealand’s Kermadec Islands, where it is known from Raoul Island and Macauley Island.

Height:
Fronds 30–80 cm high, with the rhizome occasionally forming a caudex up to 10 cm tall

Width:
Approximately 40–80 cm

Flowering:
Not applicable—spore-producing fern

Fruiting:
Not applicable—spore-producing fern

Uses:
• Container cultivation
• Warm-climate fern gardens
• Coastal gardens
• Conservatories and sheltered courtyards
• Botanical collections
• Kermadec Island-themed plantings

Appearance:
Growth habit:
An evergreen terrestrial fern forming an upright to spreading clump. Fertile and sterile fronds are similar, although fertile fronds tend to stand more erect while sterile fronds may arch or lie closer to the ground.

Rhizome:
The rhizome is erect and densely covered with black scales. Older plants may develop a short trunk-like caudex up to approximately 10 cm tall. Short rhizome branches allow the plant to expand vegetatively.

Stipes:
Stipes are generally 15–20 cm long and bear sparse brown scales and fine hairs. They often become nearly hairless as they mature, although scales may persist around the base.

Fronds:
Fronds are bright green to medium green, elliptic to narrowly elliptic and 12–60 cm long by 10–20 cm wide. They are slightly leathery to firmly fleshy but are softer and less harsh than those of several related rasp ferns. Emerging fronds are always green.

Pinnae:
The fronds bear approximately 20–46 pairs of narrow pinnae. The lower pinnae may be shortly stalked or only partly fused to the rachis, while those toward the middle and tip are directly attached and increasingly decurrent. The longest pinnae may reach 18 cm.

Spores:
The sori are discrete and arranged in one or two rows on either side of the pinna midrib. They are protected by narrow, usually linear indusia. Spores are dispersed by wind.

Ecology:
Kermadec Rasp Fern is a characteristic ground fern of the relatively dry Kermadec pōhutukawa forests of Raoul Island. Its fronds contribute cover and structure to the forest floor, while its rhizomes help anchor it among rocks, litter and shallow soils. Vegetative branching allows established plants to form expanding clumps.

Associated habitats:
Kermadec pōhutukawa forest, Kermadec ngaio scrub, coastal forest, rocky slopes, shaded cliffs, dry forest floors and deep leaf-litter communities.

How to grow:
Plant in a warm, sheltered position with free-draining soil. It tolerates a range of soil types but performs poorly where the roots remain continually wet. Water moderately during active growth and allow the surface of the soil to dry slightly between watering. Protect from frost and cold winter winds. It also grows particularly well as a container plant.

Propagation:
Easily propagated from fresh spores, which germinate readily under warm, humid conditions. Established plants may also be divided where the rhizome has naturally branched. Young plants should be kept warm, lightly shaded and evenly moist without becoming waterlogged.

Cultural use:
No specific traditional Māori uses are widely recorded. The species has considerable botanical and conservation value as a naturally range-restricted fern found only in the Kermadec Islands. The genus commemorates Samuel Doody, a seventeenth-century London apothecary and curator.

Garden value:
A handsome subtropical fern valued for its broad, fresh green fronds and tidy upright growth. It makes an excellent pot specimen or feature fern in warm, sheltered gardens. Its limited natural distribution also makes it especially desirable for specialist collections of New Zealand island flora.