Introduction & Discovery

Dicksonia sellowiana is the great tree fern of the Brazilian Atlantic Forest, a species of towering physical presence and profound economic and conservation significance whose story encompasses colonial exploitation, industrial-scale harvesting, international trade regulation, and ongoing efforts at habitat protection. Known throughout Brazil as xaxim or samambaiacu, this species develops a massive trunk reaching 10 metres or more in height, densely mantled with a thick layer of fibrous adventitious roots that for centuries made it one of the most commercially valuable fern species on Earth. The fibrous trunk material, universally called xaxim fibre in the horticultural trade, was harvested on an industrial scale throughout the twentieth century for use as a growing substrate for orchids, bromeliads, and other epiphytes. Sliced into pots, plaques, totems, and hanging baskets, xaxim fibre became the standard mounting material for tropical epiphyte cultivation worldwide, prized for its moisture-retentive yet airy texture and its resistance to decomposition. The toll of this harvest was devastating. Millions of mature tree ferns were felled across the Atlantic Forest of southern Brazil, a biome already reduced to less than 12 percent of its original extent by agricultural clearing. By the late twentieth century, wild populations of D. sellowiana had collapsed across much of their former range, prompting international alarm and regulatory action. In 2004, the species was listed on CITES Appendix II, requiring export permits and monitoring of international trade. Brazil subsequently imposed internal restrictions on harvest and commerce, and the horticultural trade pivoted to substitute materials including coconut coir fibre, sustainably harvested tree fern fibre from other genera, and synthetic alternatives. Despite these protections, illegal harvesting continues in remote areas, and the species remains a flagship for Atlantic Forest conservation. Taxonomically, D. sellowiana was described by Carl Friedrich Philipp von Martius and named in honour of Friedrich Sellow, a German naturalist and prolific collector who spent years documenting the Brazilian flora before his untimely death by drowning in the Rio Doce in 1831. The species belongs to the family Dicksoniaceae, distinguished from Cyatheaceae by hairs rather than scales and by marginal bivalved sori, and represents the Neotropical radiation of this fundamentally Gondwanan genus.

A large, robust tree fern with a thick trunk covered in a dense layer of dark brown, wiry roots that reaches a height of as much as 10 m. The ascending crown holds numerous lightly arching leaves. Dicksonia sellowiana is widespread in rain and cloud forests from southern Mexico through Central America and along the Andes to Argentina and southern Brazil from moderate elevations to 3100 m. It is similar to Dicksonia antarctica but little known in cultivation despite being one of the hardiest tree ferns and easily grown in most warm temperate climates.

Discovery & Naming

Dicksonia sellowiana was formally described by Carl Friedrich Philipp von Martius in his Flora Brasiliensis, published in instalments from the 1840s onward, based on collections made by Friedrich Sellow (also spelled Sello), a German naturalist who spent 17 years collecting plants in Brazil from 1814 until his death by drowning in the Rio Doce in 1831. Sellow's vast collections, numbering over 12,000 specimens, were sent to the Berlin Herbarium and formed the basis for numerous new species descriptions by Martius, Endlicher, and other nineteenth-century botanists. The specific epithet sellowiana honours Sellow's extraordinary contribution to Brazilian botany. The species had undoubtedly been known to indigenous peoples and Portuguese colonists for centuries before scientific description, and its fibrous trunk was in local use as a planting substrate and construction material well before European nomenclatural recognition. Throughout the twentieth century, D. sellowiana was taxonomically stable, consistently placed in Dicksonia within the Dicksoniaceae. Molecular phylogenetic studies in the twenty-first century have confirmed this placement and positioned the species within a Neotropical clade of the genus, consistent with the Gondwanan vicariance history of the family. The species' conservation crisis and CITES listing in 2004 brought it to international prominence far beyond the usual reach of pteridological taxonomy.

Native Range & Distribution Map

Distribution map showing the native range of Dicksonia sellowiana.

Biology & Frond Morphology

Dicksonia sellowiana belongs to the genus Dicksonia in the family Dicksoniaceae, producing evergreen to semi-evergreen, bipinnate to tripinnatifid fronds of large to very large size, commonly 2 to 3 metres long and in exceptional specimens reaching 3.5 metres. blades are broadly lanceolate to ovate, bright to dark green above, paler beneath, with a herbaceous to slightly leathery texture. stipe bases are densely clothed with long, stiff, dark brown to reddish-brown hairs characteristic of the family dicksoniaceae, which are diagnostic against the scaly stipe bases of cyatheaceae tree ferns. pinnae number 20 to 40 pairs, are lanceolate and deeply pinnatifid to pinnate, with ultimate segments bearing finely serrate margins. sori are marginal, protected by bivalved indusia. the crown of fronds forms a broad, spreading canopy atop the trunk, and persistent dead fronds often form a skirt below the living crown before eventually falling away. new croziers emerge densely covered in the characteristic brown hairs. 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 sellowiana 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 sellowiana 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 critical error is confusing this species with Dicksonia antarctica and expecting equivalent cold hardiness. D. sellowiana is significantly less frost-tolerant and will be killed by the moderate frosts that D. antarctica survives. Allowing the trunk to dry out during establishment or drought is frequently fatal, as the fibrous trunk depends on maintained moisture for root function. Planting in full sun causes severe frond scorch and trunk desiccation. Using alkaline soil or tap water with high pH causes chlorosis and poor growth. Purchasing wild-harvested material of unknown provenance risks supporting illegal trade and violating CITES regulations; always verify that plants or fibre are legally sourced and accompanied by appropriate documentation. Overfertilising with high-nitrogen products promotes soft growth susceptible to pests and cold damage. Failing to provide adequate drainage despite the species' moisture requirements leads to root rot.

Seasonal Considerations

Spring (September to November in the Southern Hemisphere): peak growth period. Emerging croziers unfurl and fronds expand rapidly. Increase watering frequency, begin monthly feeding with dilute balanced fertiliser, and renew mulch around the trunk base. Monitor for frost damage on new growth in areas with late spring frosts. Summer (December to February): maintain abundant moisture by deep watering every two to three days and daily trunk hosing. Provide shade from intense sun. Watch for heat stress symptoms including frond wilting and tip burn. Spores ripen during this period. Autumn (March to May): growth rate slows. Taper fertiliser applications. Continue regular watering until rains establish. Apply additional mulch before winter. Remove dead or damaged fronds. Winter (June to August): protect the crown from frost with fleece or hessian in marginal climates. Reduce watering but do not allow the trunk to dry completely. Remove any frost-damaged fronds in late winter before new growth begins.

Diseases & Pests

Common issues affecting Dicksonia sellowiana 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 sellowiana 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 sellowiana 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 sellowiana is listed on CITES Appendix II, which requires that all international trade in the species be regulated through a permit system to ensure that exports are not detrimental to wild populations. This listing, enacted in 2004, was a direct response to decades of massive commercial harvesting of xaxim fibre from wild-harvested trunks in Brazil, which devastated populations across the Atlantic Forest. Within Brazil, the species is listed as Endangered by the national red list (Lista Nacional Oficial de Especies da Flora Ameacadas de Extincao) and harvest from wild populations is prohibited under federal law, though enforcement is imperfect in remote forested areas. The IUCN Red List currently assesses the species as globally Endangered. The Atlantic Forest biome itself has been reduced to approximately 12 percent of its original extent, and the loss of old-growth forest where the largest and oldest specimens occur is ongoing. Reforestation and restoration programmes in southern Brazil include D. sellowiana as a target species, but the slow growth rate means that ecological recovery of mature tree fern populations is a matter of centuries rather than decades. Substitute materials for xaxim, including coconut coir fibre, osmunda fibre, cork, and synthetic alternatives, are now promoted throughout the global orchid and bromeliad community to reduce demand for wild-harvested material.

Collector Notes

Dicksonia sellowiana is a must-have species for the serious tree fern collector and a powerful conservation statement plant. All acquisition must comply with CITES Appendix II regulations; plants should be accompanied by phytosanitary certificates and CITES permits where applicable. Nursery-propagated material from spore is the ethical and legal choice. Specialist tree fern nurseries in Australia, New Zealand, and Europe occasionally offer spore-raised plants, and the species is increasingly available from Brazilian nurseries engaged in conservation-oriented propagation. Provenance information documenting the source population is particularly valuable given the species' wide geographic range and likely genetic diversity. Notable specimens in public collections include plantings at the Jardim Botanico do Rio de Janeiro, the Jardim Botanico de Curitiba, and in European collections at the Royal Botanic Gardens Kew, the Royal Botanic Garden Edinburgh, and Trebah Garden in Cornwall. Collectors should document their plants with photographs, measurements, and growth records to contribute to the horticultural knowledge base for this conservation-critical species.

Ethnobotany & Cultural Significance

The cultural and economic significance of Dicksonia sellowiana in Brazil is immense and multifaceted. For centuries, the fibrous trunk material known as xaxim was harvested by rural communities for a range of domestic uses, including as a moisture-retentive planting substrate for orchids and other epiphytes, as pot-making material (vasos de xaxim), and as building insulation. From the mid-twentieth century onward, commercial exploitation escalated dramatically as the global orchid-growing industry adopted xaxim fibre as the preferred epiphyte mounting and potting substrate. Entire mountainsides in southern Brazil were stripped of their tree ferns to supply an international market. Trunks were sawn into sections and either shipped whole or shredded into fibre for potting mixes. The economic value of this trade was substantial, supporting rural livelihoods even as it destroyed the ecological resource base. Indigenous Guarani and other forest-dwelling peoples traditionally used the starchy trunk pith as an emergency food and the hairs for wound dressing. In modern Brazilian culture, the xaxim has become a symbol of environmental destruction and the need for sustainable resource management, featuring prominently in environmental education programmes. The shift to alternative substrates since the CITES listing has been largely successful in the formal market, though informal and illegal harvesting persists.

Frequently Asked Questions