Dieffenbach's Spear

Aciphylla dieffenbachii

Not Threatened

Aciphylla dieffenbachii , known as Dieffenbach's speargrass, is one of New Zealand's most range-restricted speargrasses, endemic to the Chatham Islands where it represents one of only two Aciphylla species found on these remote islands. Named after Ernst Dieffenbach, the naturalist who first collected it in 1840, this impressive species forms substantial rosettes of viciously sharp leaves in coastal to subalpine habitats. Unlike its mainland relatives that inhabit high mountains, this species has adapted to the oceanic climate of the Chathams, growing from sea level to the highest points on the islands (around 300 meters). The evolution of speargrasses on these isolated islands, 800 kilometers east of mainland New Zealand, represents a fascinating example of island biogeography. This species is culturally significant to Moriori and Māori of Rēkohu (Chatham Islands) and plays an important role in the unique island ecosystems of this remote archipelago.

Close view of the spiny foliage typical of Aciphylla speargrasses — Image credit: Dieffenbach's Spear ( *Aciphylla dieffenbachii* ) - Photo by Wikipedia contributors, via Wikipedia

Plant Description

Aciphylla dieffenbachii forms impressive rosettes of rigid, pinnately divided leaves that can create clumps over one meter across in optimal conditions. Individual leaves reach 20-45 cm long and 10-25 mm wide, divided into 5-9 pairs of segments plus a prominent terminal segment. Each segment ends in an extremely sharp, yellowish spine capable of penetrating thick clothing and gumboots. The leaves are thick, leathery, and blue-green to gray-green with distinctive yellow or orange margins.

The species develops a stout, woody rootstock with a deep taproot extending up to 1.5 meters, anchoring the plant against the fierce winds that regularly batter the Chatham Islands. Lateral roots spread extensively, allowing the plant to access moisture and nutrients across a wide area. The crown accumulates persistent dead leaves that form a protective thatch around the living rosette.

Flowering occurs from November to January, earlier than most mainland species due to the milder oceanic climate. Plants are dioecious with separate male and female individuals. The inflorescences rise 40-80 cm tall, bearing compound umbels of small cream to yellowish flowers. Male plants produce more numerous, showier flower heads. The flowers emit a sweet, honey-like fragrance that attracts the limited pollinator fauna of the islands. Seeds are relatively large achenes, 7-10 mm long with prominent wings, adapted for wind dispersal across the treeless landscapes of the Chathams.

Quick Facts

*Aciphylla dieffenbachii* quick facts
Scientific Name	Aciphylla dieffenbachii
Height	40-80 cm rosettes; flowering stems to ~80 cm
Spread	60-120 cm clumps in mature stands
Water Needs	Moderate - adapts from moist peat to freely drained slopes
Light	Full sun and wind-exposed coastal light
Frost Tolerance	Moderate; tolerates light frosts but prefers mild winters
Salt Tolerance	High - naturally endures Chatham Island salt spray
Growth Rate	Moderate; rosettes enlarge steadily in oceanic climates
Lifespan	Long-lived perennial (many years)

Climate Best Suited to

Cool-summer districts with strong airflow and rapid drainage; avoid humid heat.

Regional Suitability

City suitability for *Aciphylla dieffenbachii*
City	Climate Suitability
Queenstown	Ideal
Wānaka	Ideal
Twizel	Ideal
Christchurch	Moderate
Wellington	Moderate
Auckland	Marginal
Dunedin	Excellent
Hamilton	Challenging - requires cool conditions
Tauranga	Challenging - requires cool conditions
Napier	Challenging - requires cool conditions
Palmerston North	Good
Nelson	Good
Invercargill	Excellent
New Plymouth	Challenging - requires cool conditions
Rotorua	Challenging - requires cool conditions
Whangārei	Challenging - requires cool conditions
Whangārei	Suitable
Gisborne	Suitable
Whanganui	Suitable

Plant Habitat

Aciphylla dieffenbachii occupies diverse habitats across the Chatham Islands, from coastal cliffs to the highest peaks, though it is most abundant in open grasslands and peat bogs. The species thrives in the islands' hyperoceanic climate, characterized by cool summers (average 16°C), mild winters (average 9°C), and persistent strong winds. Annual rainfall of 800-1000mm is distributed fairly evenly throughout the year.

Soil preferences are remarkably broad, growing in everything from free-draining volcanic soils to waterlogged peat. The species shows particular abundance in the unique Chatham Island schist-derived soils and in the extensive peat accumulations that characterize much of the islands' interior. It tolerates salt spray in coastal locations, unusual for a speargrass.

The species often dominates in the distinctive vegetation communities of the Chathams. It grows with endemic species like Myosotidium hortensia (Chatham Island forget-me-not), Astelia chathamica , and Dracophyllum arboreum . In peat bogs, it associates with Sporadanthus traversii and various sedges. The absence of mammalian browsers until human arrival allowed the evolution of plant communities where spiny defenses were less crucial, though A. dieffenbachii retained its formidable armament.

Plant Conservation

Listed as 'At Risk - Naturally Uncommon' due to its restricted island distribution, Aciphylla dieffenbachii faces several conservation challenges. While still locally common in suitable habitat, the total population is limited by the small land area of the Chatham Islands (roughly 1000 square kilometers).

Introduced mammals pose significant threats. Sheep, cattle, and pigs damage plants through trampling and rooting. Possums, introduced in the early 1900s, browse young plants before spines fully develop. Habitat modification for agriculture has eliminated many lowland populations, confining the species increasingly to reserves and inaccessible areas.

Climate change impacts are uncertain but concerning. The Chatham Islands' climate is strongly influenced by ocean currents and weather patterns that may shift with global warming. Increased storm intensity could cause erosion and habitat loss, while temperature changes might affect the species' competitive relationships with other plants.

Conservation efforts include habitat protection, control of invasive mammals, and ex-situ cultivation in mainland botanic gardens. The species' cultural significance adds importance to its conservation, as it features in traditional Moriori and Māori practices.

Growing Requirements

Soil

Gritty, mineral soils; plant high among rocks for rapid runoff.

Light

Full sun, high light exposure.

Water

Low to moderate; keep crowns dry in winter.

Planting Guide

Best Planting Practices

Use thick gloves; avoid close proximity to paths due to sharp spines. Successful establishment requires careful attention to site preparation, timing, and ongoing care. Consider local climate conditions and soil characteristics when selecting planting locations. Regular monitoring during establishment ensures the best outcomes for long-term plant health and development.

Ecological Role

Environmental Benefits

Aciphylla dieffenbachii is a keystone species in Chatham Island ecosystems, providing structure and habitat in otherwise uniform grasslands and bogs. The large rosettes create microhabitats with moderated temperatures and humidity, supporting endemic invertebrates including several species found nowhere else.

The species has co-evolved with the unique Chatham Islands fauna. With no native land mammals and few reptiles, the pollinator community consists primarily of flies, beetles, and the endemic Chatham Island red admiral butterfly. The large seeds provide food for the endemic Chatham Island pigeon and other birds, which may also contribute to seed dispersal despite the wind-dispersal adaptations.

The accumulation of dead leaves around rosettes contributes significantly to soil organic matter in nutrient-poor habitats. This process is particularly important in peat bogs where the species helps maintain the distinctive bog chemistry and hydrology. The deep roots also play a role in nutrient cycling, bringing minerals from depth and depositing them at the surface through leaf litter.

The species serves as a flagship for Chatham Islands conservation, its dramatic appearance making it an effective symbol for protecting the islands' unique biodiversity.

Uses

Traditional and Modern Applications

A spectacular specimen for coastal gardens and cool-climate landscapes, prized for its dramatic blue-green foliage and impressive flower spikes. In the Chatham Islands, it is a key component of restoration planting in sand dunes and coastal peatlands. Its relatively softer spines compared to mainland species make it a slightly safer, though still formidable, architectural feature for public gardens.

Landscaping Uses

Garden Design Applications

Excellent for rock gardens, alpine collections, and naturalistic plantings. Best used in open, well-drained positions where its distinctive form can be appreciated. Combines well with other native alpine plants and provides year-round structure. Consider placement carefully due to sharp foliage - avoid high-traffic areas. Creates dramatic focal points in contemporary and native-themed garden designs.

Seasonal Care

Year-Round Maintenance

Spring management focuses on removing winter-damaged foliage and assessing drainage. Summer care emphasizes maintaining adequate moisture without waterlogging. Autumn preparation includes reducing irrigation and ensuring good air circulation. Winter protection may require covering in areas subject to excessive moisture. Year-round monitoring ensures early detection of problems and maintenance of optimal growing conditions.

Pruning

Pruning Techniques

Minimal maintenance is required beyond the removal of spent flower stalks, which can persist for many months. Old leaves eventually form a dry skirt which naturally protects the rootstock; however, in garden settings, these can be carefully trimmed away for a tidier appearance. Always wear gloves, as even 'soft' speargrass spines can cause injury.

How to Grow Dieffenbach's Speargrass

From Seed

Propagation from seed is the primary and most successful method for Aciphylla dieffenbachii . This Chatham Island endemic produces abundant seed which, unlike some mainland species, often germinates readily if sown fresh. Seed should be collected as soon as the seed heads dry and turn brown, typically in late summer (January to February).

Sow the seeds in trays using a standard seed sowing mix lightened with perlite or pumice to ensure drainage. Cover lightly. While fresh seed may germinate within a few weeks in autumn, some may wait until spring. The seedlings of this species are vigorous compared to high-alpine relatives.

Prick out seedlings into individual pots once the first true leaves appear. They grow relatively quickly and can often be planted out into their final positions in their second year. Because this species is vulnerable to sudden collapse or root rot, it is wise to keep a few young plants in reserve if you are maintaining a collection.

From Division

Division is not commonly practiced with Aciphylla dieffenbachii because the plant typically forms a single main rosette or a tight cluster that relies on a sensitive taproot system. Furthermore, older plants can be short-lived, often dying after a prolific flowering event (monocarpic tendency), so reliance on vegetative perpetuation of old plants is risky.

If a plant does produce multiple distinct side shoots with their own root systems, these can be carefully detached in spring. As with all speargrasses, cleanliness is vital; use sterile tools and apply a fungicide to cut surfaces. However, seed remains the preferred method for renewing stock.

Cultivation Requirements

In cultivation, Dieffenbach's Speargrass requires different treatment from the hardier alpine species. Coming from the Chatham Islands, it prefers a maritime climate: cool, moist summers and mild winters. It is not as frost-hardy as mainland alpine species and may suffer in severe inland frosts.

It thrives in deep, fertile, but well-drained soil-often much richer than the scree needed for other speargrasses. It is particularly fond of sandy, peaty soils that hold moisture but do not become waterlogged. Full sun is essential for good health and leaf colour.

A major challenge in cultivation is its susceptibility to root rot and sudden death, especially in hot, humid climates. Good airflow is essential. It is also highly palatable to weevils and other pests which can bore into the crown; regular inspection is recommended. Despite these challenges, its dramatic, soft-green foliage and impressive golden flower spikes make it a prized specimen for coastal and cool-climate gardens.

Pests & Diseases

On the Chatham Islands, Aciphylla dieffenbachii faces threats primarily from introduced mammals rather than invertebrate pests or diseases. The isolation of the islands means many mainland pests are absent.

In cultivation on mainland New Zealand, the species proves more susceptible to problems than in its native habitat. Crown rot can develop in humid conditions, particularly in warmer regions. The oceanic adaptation means the species is less tolerant of extreme temperatures and drought than mainland species.

Scale insects and mealybugs occasionally infest cultivated plants, particularly those stressed by inappropriate growing conditions. These pests seem more problematic on this species than on mainland speargrasses, possibly due to differences in chemical defenses.

Weevils that typically attack mainland Aciphylla species may colonize A. dieffenbachii in cultivation, though it's not their preferred host. Regular monitoring allows early detection and manual removal.

The main challenge in cultivation is providing the cool, humid, wind-exposed conditions the species requires without the extreme cold of alpine habitats. Success is greatest in coastal areas with mild, moist climates similar to the Chatham Islands.

Cultural Significance

Traditional Uses and Values

Dieffenbach's Speargrass (speargrass or 'Spaniard') holds significant cultural meaning for Māori, who called these plants 'taramea' and used them as landmarks for navigation and seasonal calendars. The fierce spines provided protection for settlements and were incorporated into traditional stories and whakataukī (proverbs). Early European settlers named them 'Spaniards' due to their resemblance to defensive spears. Today, these plants symbolize the wild character of New Zealand's high country and represent the adaptation of endemic species to harsh environments. They remain important cultural markers in traditional Māori knowledge systems and continue to feature in contemporary conservation and restoration efforts.

Bonus Tip

Dieffenbach's Speargrass ( Aciphylla dieffenbachii ) is well-adapted to New Zealand conditions and often performs better with minimal intervention rather than intensive care.