Chatham Island Grass Tree

Botanical name: Dracophyllum arboreum
Synonyms: Dracophyllum latifolium var. ciliolatum, Dracophyllum scoparium var. major
Common name(s): Chatham Island Grass Tree, Tarahinau

About:
Chatham Island Grass Tree is a distinctive forest tree endemic to the Chatham Islands. It can form a substantial tree up to 18 m tall and is notable for its dramatically different juvenile and adult foliage. Young plants carry broad, grass-like leaves, while mature trees develop much shorter, narrow leaves resembling coarse needles. Small white flowers are produced in compact spikes, partly hidden by persistent, hard, sharply pointed floral bracts.

Natural habitat:
An important component of Chatham Islands forest, particularly inland on deep, damp peaty soils. It occurs in lowland and upland forest, shrubland, swamp margins, gullies, stream sides, cliffs and the transition between forest and restiad bog. In favourable sites it may become the dominant canopy tree.

Growing environment:
Prefers cool, humid conditions and acidic, permanently damp, peaty soil that does not remain deeply waterlogged. It grows in full sun or light shade and tolerates the strong winds, salt-laden air and cool maritime climate of the Chatham Islands. Young plants require reliable moisture and shelter from excessive heat and drying winds.

Endemic distribution:
Endemic to New Zealand’s Chatham Islands, where it occurs on Rēkohu/Chatham Island, Rangiuria/Pitt Island and Rangatira/South East Island.

Height:
4–18 m

Width:
Approximately 3–8 m, depending on exposure and growing conditions

Flowering:
Flowers may be present throughout the year, with the main display generally occurring from spring to summer.

Fruiting:
Fruit may be present throughout the year.

Uses:
• Chatham Islands ecological restoration
• Specialist native collections
• Cool-climate woodland planting
• Shelter and canopy establishment
• Botanical and conservation gardens
• Large specimen tree in suitable climates

Appearance:
Growth habit:
A medium-sized to tall evergreen tree with a dense, often irregular crown. In exposed sites it may remain shorter and windswept, while sheltered forest specimens can develop into tall canopy trees. It may occasionally begin life as an epiphyte in a tree fern before extending roots to the ground.

Trunk/Bark:
Older trunks and branches have greyish-brown to brown bark that is finely fissured. Young stems range from yellowish-brown to reddish-brown.

Juvenile leaves:
Juvenile foliage is crowded near the branch tips and spreads outward. The leaves are 10–22 cm long and 1–1.8 cm wide, broad, linear-triangular and leathery. They are yellow-green to light green, with smooth surfaces and densely hairy margins. Juvenile foliage may occasionally reappear as reversion shoots on mature trees.

Adult leaves:
Adult leaves are much shorter and narrower, generally 2.5–9 cm long and only 1–2 mm wide. They are linear to narrowly triangular, spreading and grass-like, with densely hairy margins and a small tuft of rough hairs near the base of the upper surface.

Flowers:
Small white flowers are borne in dense terminal spikes 1.5–3.8 cm long on short lateral branchlets. Each spike contains approximately four to nine sessile flowers. The flowers have cylindrical white corolla tubes with short reflexed lobes and are partly concealed by persistent, pointed floral bracts. Pink or reddish tones may occur in the bracts or surrounding floral structures.

Fruit:
The fruit is a very small, dark brown, oblong capsule approximately 1.2–1.5 mm long. Each capsule contains minute yellowish-brown seeds.

Ecology:
Tarahinau is a major structural species in Chatham Islands forests, especially on deep peaty soils away from the coast. Its dense canopy provides shelter in an exceptionally windy maritime environment and contributes litter and organic matter to peat-rich forest floors. The minute seeds are dispersed by wind.

Its contrasting juvenile and adult foliage is an adaptation known as heteroblasty. The narrow adult leaves are likely better able to withstand the persistent strong winds of the Chatham Islands than the much broader juvenile foliage.

Where forest grades into restiad bog, Tarahinau may grow alongside Dracophyllum scoparium. The two species frequently hybridise in disturbed or overlapping habitats.

Associated habitats:
Peaty lowland forest, upland forest, restiad bog margins, swamp forest, shrubland, gullies, stream margins, cliffs and windswept tablelands. Associated plants may include Chatham Island ribbonwood, rautini, Chatham Island tree ferns, Muehlenbeckia australis, Olearia chathamica, Olearia semidentata, Coprosma species and Dracophyllum scoparium.

How to grow:
Plant in a cool, sheltered position with acidic, humus-rich, peaty soil. Keep the root zone consistently moist but avoid stagnant waterlogging. Partial shade is beneficial for young plants, although established trees will tolerate full sun in cool climates. Mulch with leaf mould or fine bark to conserve moisture and maintain an acidic soil environment.

Tarahinau is difficult to maintain in warm or dry districts and is best suited to specialist collections, cool coastal gardens or environments that closely resemble the climate of the Chatham Islands.

Propagation:
Can be propagated from fresh seed. Sow the minute seeds on the surface of an acidic, free-draining seed mix and do not bury them deeply. Maintain high humidity, cool temperatures and consistent moisture. Seedlings are slow-growing and can be difficult to maintain, particularly if exposed to heat, drought or alkaline soil.

Cultural use:
Tarahinau is the Moriori name for this characteristic Chatham Islands tree. It is an important part of the natural and cultural landscape of Rēkohu and has strong significance as a dominant species within the islands’ remaining indigenous forests.

The botanical name Dracophyllum means “dragon leaf”, referring to the resemblance of its foliage to that of dragon trees, while arboreum means “tree-like”.

Garden value:
A remarkable and highly distinctive tree for specialist native collections. Its changing foliage, strong architectural form and Chatham Islands provenance give it exceptional botanical interest. It is most successful in cool, damp, acidic gardens where its natural peatland forest conditions can be closely reproduced.