Introduction & Discovery

Dicksonia squarrosa, known in New Zealand by its Maori name wheki, is the most abundant and widespread tree fern in the New Zealand archipelago and one of the most distinctive, characterised by its slender dark trunks, wiry black stipe bases, compact upright crown, and extraordinary capacity to form multi-trunked colonies from basal suckers. This last feature is highly unusual among tree ferns, the great majority of which grow as solitary individuals from a single apical meristem, and it gives D. squarrosa a unique ecological and visual profile: mature colonies of interconnected trunks rising in dark-barked clusters from the forest floor, creating a grove-like effect that is one of the most evocative sights of the New Zealand bush. The species belongs to the family Dicksoniaceae, sharing with its congeners the diagnostic features of multicellular hairs rather than scales on the stipe bases and marginal bivalved sori, characters that separate the family from the more species-rich Cyatheaceae. Among New Zealand's native tree ferns, which include the spectacular silver fern Cyathea dealbata, the massive mamaku Cyathea medullaris, and the graceful ponga Cyathea dealbata, D. squarrosa is the tough generalist: found from the subtropical north to the cool temperate south, from sea level to the montane forest limit, from sheltered valley floors to wind-blasted hillsides. Its resilience and abundance have given it a long history of human use. Maori traditionally used the fibrous trunk for fencing, building walls, and lining food pits, and the dark wiry stipe bases for lashing and binding. European settlers continued to use the trunks for fencing and garden borders, a practice that persists in some rural areas. In contemporary horticulture, D. squarrosa is increasingly valued as a hardy, characterful tree fern for temperate maritime gardens worldwide, offering the distinctive multi-trunk habit that no other cultivated tree fern can provide.

A medium-sized tree fern from New Zealand, where it is commonly found in a variety of lowland and montane forest habitats, often in wet situations. Its range extends from the Three Kings Islands over the North and South Islands to Stewart Island and the Chatham Islands. Dicksonia squarrosa forms a slender, sometimes branching trunk to about 7 m (23 ft.) tall, covered in persistent leaf bases. The crown is relatively small and the leaves are held by slender, blackish, hairy leafstalks. It is one of the most easily grown tree ferns and well suited to a variety of temperate climates, where it will hold up to moderate freezes.

Discovery & Naming

Dicksonia squarrosa was first described by the German-born botanist Georg Forster in 1786, based on material collected during Captain James Cook's second voyage to the Pacific in 1772 to 1775. Forster, who accompanied his father Johann Reinhold Forster as naturalist on the voyage, documented numerous new plant species from New Zealand and the Pacific islands, and D. squarrosa was among the earliest New Zealand ferns to receive a formal scientific name. The epithet squarrosa refers to the spreading or recurved nature of the pinnae or frond segments. The species was subsequently treated by Joseph Dalton Hooker in his Flora Novae-Zelandiae of 1853 to 1855 and by Thomas Kirk in the Students' Flora of New Zealand in 1899, both of whom confirmed its distinctness and widespread occurrence throughout the archipelago. Twentieth-century revisions of the New Zealand tree fern flora by E. J. Brownsey and J. C. Smith-Dodsworth provided detailed morphological descriptions and distribution data. Molecular phylogenetic studies in the twenty-first century have confirmed the placement of D. squarrosa within Dicksoniaceae and its sister relationship to other Australasian Dicksonia species, consistent with a Gondwanan origin and vicariance-driven speciation following the separation of New Zealand from Australia and Antarctica.

Native Range & Distribution Map

Distribution map showing the native range of Dicksonia squarrosa.

Biology & Frond Morphology

Dicksonia squarrosa belongs to the genus Dicksonia in the family Dicksoniaceae, producing evergreen, bipinnate to tripinnatifid fronds of moderate size, typically 1 to 2 metres long, rarely exceeding 2.5 metres. blades are lanceolate to narrowly lanceolate, dark green above and distinctly paler, almost glaucous beneath, with a firm, slightly leathery texture. stipe bases are diagnostic: slender, wiry, almost black in colour, and densely clothed with stiff dark brown to blackish hairs at the base, transitioning to shorter hairs along the stipe length. these dark, wiry stipe bases are a key field character that distinguishes d. squarrosa from other new zealand tree ferns at a glance. pinnae are relatively closely spaced and deeply pinnatifid. sori are marginal, enclosed in the bivalved indusia characteristic of the genus. old fronds are deciduous, falling cleanly from the trunk rather than forming a persistent skirt, which combined with the slender dark trunk gives the species a distinctive clean-lined silhouette. the crown is relatively compact and upright compared to the spreading crowns of cyathea dealbata or c. medullaris. fronds that unfurl from coiled fiddleheads (croziers). Like all ferns, it reproduces via spores borne on the underside of fertile fronds rather than flowers and seeds, and its life cycle alternates between a dominant sporophyte (the visible plant) and a small, short-lived gametophyte stage.

Reproduction & Propagation

Propagation of Dicksonia squarrosa can be achieved through several methods:

• Spores: Collect ripe spores from the underside of fertile fronds, sow on sterilised peat or peat/perlite mix. Do not cover. Keep humid and in bright indirect light. Prothalli (gametophytes) typically develop in 4–12 weeks, and young sporophytes appear after a further 2–6 months.
• Division: Mature clumps with multiple crowns or creeping rhizomes can be divided in spring as new fronds emerge.
• Rhizome cuttings / offsets: Epiphytic genera (Davallia, Polypodium, Phlebodium) can be propagated from 5–10 cm rhizome segments with at least one frond and visible roots.

Cultivation & Substrate

Successful cultivation of Dicksonia squarrosa depends on matching three conditions to its natural habitat: consistent moisture without waterlogging, a humus-rich yet well-drained substrate, and the correct light level for its frond type — whether dappled woodland shade, bright filtered light, or, for a handful of rock ferns, direct sun.

Common Mistakes to Avoid

The most common error is planting D. squarrosa in hot, dry, continental climates where it suffers from summer heat and low humidity. While hardier than most tree ferns, it is fundamentally a cool maritime species that performs best where summers are mild and humid. Failing to allow adequate space for colony development is another frequent mistake; the suckering habit means a single plant can spread to cover several square metres over time, and crowding results. Planting in waterlogged soil causes crown rot despite the species' moisture tolerance. Confusing D. squarrosa with D. antarctica and expecting identical growth form leads to disappointment, as D. squarrosa has a very different habit with slender dark trunks and a compact crown. Attempting to suppress the suckering habit by removing basal shoots weakens the colony and reduces the very feature that makes the species distinctive. Applying alkaline amendments such as lime to the soil causes chlorosis.

Seasonal Considerations

Spring (September to November): peak growth period. Remove winter-damaged fronds before new croziers emerge. Apply a light topdressing of balanced slow-release fertiliser. Renew mulch. Water deeply if spring rainfall is sparse. This is the best time for planting, dividing colonies, or transplanting. Summer (December to February): maintain consistent moisture through deep watering every five to seven days during dry spells. Overhead watering of trunks benefits the colony. Monitor for heat stress in exposed positions. Collect spores from mature fronds if propagation is desired. Autumn (March to May): growth slows. Continue watering until autumn rains establish. Apply additional mulch before winter. Detach and transplant basal suckers for propagation. Winter (June to August): minimal care in mild climates where the species is evergreen. In frost-prone areas, protect crowns of young plants with fleece. Remove frost-damaged fronds in late winter. Avoid root zone disturbance.

Diseases & Pests

Common issues affecting Dicksonia squarrosa in cultivation:

• Root/rhizome rot: Caused by waterlogged substrate, compacted soil, or overwatering in cool weather. Ensure the growing medium is well-aerated and never let pots sit in standing water for prolonged periods.
• Fungal leaf spot & Botrytis: Brown or grey blotches appear in stagnant, overly humid conditions. Improve air circulation, remove affected fronds, and avoid wetting foliage late in the day.
• Scale insects & mealybugs: The most common fern pests, hiding on stipes and frond undersides. Wipe off with a cotton swab dipped in diluted isopropyl alcohol, or treat with horticultural soap. Many chemical pesticides scorch fern fronds — always test on one frond first.
• Spider mites: Fine webbing and stippled fronds, common in dry indoor air. Raise humidity and rinse fronds regularly with tepid water.
• Frond browning (tip burn): Caused by dry air, direct hot sun, fluoridated or chlorinated tap water (especially in Nephrolepis, Calathea-loving filmy ferns), or soluble-salt build-up from fertiliser. Flush the pot with rainwater and reduce feeding.

Indoor Growing & Terrariums

Dicksonia squarrosa can be grown indoors as a houseplant or terrarium subject when its humidity and light requirements are met.

Indoor Setup

• Light: Bright indirect light — an east- or north-facing window, or 30–60 cm under an LED grow light (10–12 hours/day). Most ferns scorch in direct midday sun.
• Humidity: 50–80%. Group plants, stand pots on a pebble-and-water tray, or run a humidifier; misting alone rarely raises ambient humidity enough.
• Temperature: 16–24°C (60–75°F) for most indoor species; avoid cold drafts and hot radiators.
• Substrate: Peat-free potting mix with added perlite and orchid bark for drainage; epiphytic genera (Platycerium, Davallia) grow best mounted on bark or in a bark-heavy orchid mix.
• Water: Keep consistently moist but never waterlogged. Let the top 1–2 cm of substrate dry slightly between waterings in winter.
• Air circulation: A gentle fan discourages fungal leaf spot without drying out the fronds.

Landscape & Garden Use

Dicksonia squarrosa can be used in the garden wherever its hardiness and habitat preferences are matched. Ferns are classic choices for shaded borders, woodland gardens, stumperies, rockeries, stream-side plantings, and ground-cover under trees.

Landscape Tips

• Companions: Hostas, Astilbe, Heuchera, Tiarella, Epimedium, hellebores, snowdrops and other shade-tolerant perennials are classic partners.
• Soil preparation: Incorporate leaf mould or composted bark to improve moisture retention and mimic a forest floor.
• Mulching: A 3–5 cm mulch of chipped bark or leaf litter protects the rhizomes, conserves moisture, and slowly releases nutrients.
• Watering: Establish new plantings with regular deep watering during the first growing season; most hardy ferns need only occasional supplemental irrigation once established.

Conservation & Collector Notes

Dicksonia squarrosa is globally secure and is the most abundant tree fern in New Zealand, where it is classified as Not Threatened under the New Zealand Threat Classification System. It is not listed on CITES appendices, as it falls outside the Cyatheaceae blanket listing. The species is tolerant of habitat disturbance and is a successful coloniser of degraded and secondary vegetation, traits that have maintained large populations despite extensive forest clearance in New Zealand over the past century. Populations on the Chatham Islands are more limited and potentially vulnerable to habitat changes. The principal threats to the species in New Zealand are herbivory by introduced possums, deer, and pigs, which damage croziers and suppress colony vigour, particularly in unmanaged forest areas. Climate change may alter the competitive dynamics of New Zealand forest but is unlikely to threaten this adaptable species directly. No conservation-driven restrictions on cultivation or trade apply.

Collector Notes

Dicksonia squarrosa is increasingly available from specialist fern nurseries in New Zealand, Australia, the United Kingdom, and western Europe. For the collector, its principal interest lies in the colony-forming suckering habit, which is virtually unique among cultivated tree ferns and develops into an increasingly impressive display over years and decades. Wild-provenance material from different parts of the natural range may exhibit variation in cold tolerance, vigour, and growth form. Plants from the southern South Island and Stewart Island are likely to represent the most cold-adapted genotypes. The species is represented in major public collections including the Royal Botanic Gardens Kew, the Royal Botanic Garden Edinburgh, Tresco Abbey Garden, and numerous New Zealand public gardens. The American Fern Society and British Pteridological Society spore exchanges occasionally offer spore. No formal cultivars are recognised. The species is an excellent subject for naturalistic landscape plantings where a grove effect is desired.

Ethnobotany & Cultural Significance

Dicksonia squarrosa holds a significant place in traditional Maori material culture. The fibrous trunk, known as wheki, was widely used for building construction, particularly for the walls of temporary and semi-permanent structures, food-storage pits (rua), and fencing. The soft core of the trunk was sometimes consumed as an emergency food, and the trunk served as a support for growing kumara (sweet potato). The stiff, dark, wiry stipe bases were used as bindings and lashings, and the fronds as ground cover and mulch in gardens. In contemporary Maori culture, the wheki retains cultural significance and the species features in traditional ecological knowledge relating to forest management and seasonal indicators. European settlers adopted the use of the trunks for fencing and garden borders, a practice that continues in rural New Zealand. The species is not used medicinally in any documented tradition. In the broader context of New Zealand native plants, wheki is overshadowed in popular culture by the iconic silver fern (Cyathea dealbata) but is of greater practical importance owing to its abundance and versatility.

Frequently Asked Questions