Introduction & Discovery

Phymatosorus pustulatus, the hound's tongue fern or kowaowao in the Maori language, is a robust, versatile fern of the family Polypodiaceae and one of the most familiar and widespread ferns in New Zealand. The common name hound's tongue refers to the shape of the simple fronds, which are elongated and tongue-like, though the species also produces deeply divided fronds in some conditions, adding to the diversity of form that characterizes this adaptable plant. The species has a distinguished position in New Zealand's natural and cultural history. It is one of the most recognizable native ferns, growing abundantly in forests, gardens, on rock walls, and even on urban structures throughout the country. The Maori name kowaowao is onomatopoeic, said to represent the barking sound of a dog, linking the plant to its common name through a different linguistic tradition. Maori have traditionally used the aromatic rhizome in medicinal preparations, and the plant features in various aspects of Maori cultural practice. In the wild, P. pustulatus grows as both an epiphyte and a terrestrial fern, its thick, creeping rhizome spreading over tree trunks, rocks, walls, and soil surfaces with equal ease. The rhizome is aromatic, releasing a distinctive sweet, slightly spicy fragrance when crushed, caused by volatile terpenoid compounds stored in specialized secretory cells. This aromatic quality has led to the species being called the fragrant fern in some references. For the horticulturist, Phymatosorus pustulatus is an exceptionally easy and rewarding fern to grow. Its tolerance of frost, shade, moderate drought, and a wide range of soil types makes it one of the most adaptable ferns available for temperate gardens. The species' combination of attractive foliage, fragrant rhizome, cultural significance, and undemanding nature has made it a staple of New Zealand garden design and an increasingly appreciated plant internationally.

Discovery & Naming

Phymatosorus pustulatus has been known to European science since the earliest botanical explorations of New Zealand. The species was among the ferns collected by Joseph Banks and Daniel Solander during Captain James Cook's first voyage to New Zealand in 1769–1770, and early descriptions were published in the late eighteenth and early nineteenth centuries. The taxonomic history of the species is complex. It was originally described as Polypodium pustulatum and has been transferred to numerous genera including Phymatodes, Microsorum, and Phymatosorus as generic concepts have evolved. The currently accepted placement in Phymatosorus reflects molecular phylogenetic evidence supporting the separation of this group from the core Microsorum lineage. Some recent molecular studies have suggested that New Zealand and Australian populations may represent distinct species or subspecies, and the relationship between P. pustulatus and P. diversifolius continues to be refined. The New Zealand populations are sometimes treated as a separate species, P. scandens, though this name is not universally accepted. The species has been extensively collected and is represented in all major New Zealand herbaria, including the Allan Herbarium at Landcare Research and the Te Papa herbarium, as well as in international collections at Kew, the British Museum of Natural History, and numerous other institutions.

Frond Morphology

The fronds of Phymatosorus pustulatus exhibit the heterophylly characteristic of the genus, though typically less dramatically than P. diversifolius. Simple fronds are the most common form, elongated tongue-shaped to broadly lanceolate, 15 to 40 centimeters (6–16 inches) long and 3 to 8 centimeters (1.2–3 inches) wide, with an acute to obtuse apex and a cuneate to attenuate base narrowing into the stipe. Pinnatifid fronds, with one to five pairs of lateral lobes, occur on vigorous, well-lit specimens and may reach 30 to 50 centimeters (12–20 inches) in length. The stipe is 5 to 20 centimeters (2–8 inches) long, green to straw-colored, and smooth or with a few scattered scales near the base. The lamina is coriaceous to subcoriaceous, thick and leathery in texture, with a glossy, dark green adaxial surface and a paler, matte abaxial surface. The margin is entire, slightly thickened, with a distinct cartilaginous border visible under magnification. Venation is reticulate, with prominent areolae containing free included veinlets that are clearly visible on the abaxial surface. The midrib is raised on both surfaces. Sori are round, large (2–4 millimeters in diameter), exindusiate, prominently raised on the abaxial surface to create the distinctive pustulate (bumpy or blistered) appearance referenced in the specific epithet. Sori are arranged in one to three irregular rows between the midrib and the margin, often extending over the upper two-thirds of the frond. The rhizome is thick, fleshy, 6 to 15 millimeters in diameter, long-creeping, covered with brown, lanceolate, deciduous scales. The rhizome surface is smooth and greenish when young, becoming brown and corky with age. Prominent phyllopodia mark former frond positions. The rhizome is strongly aromatic, with a sweet, spicy fragrance that is one of the plant's most distinctive features.

Native Range & Distribution Map

Distribution map showing the native range of Phymatosorus pustulatus.

Biology & Frond Morphology

Phymatosorus pustulatus is among the most ecologically successful and physiologically versatile ferns in New Zealand, occurring in habitats ranging from coastal forests to subalpine scrub and from pristine native bush to urban gardens and derelict structures. This versatility is underpinned by several key biological features. The thick, fleshy rhizome functions as a major organ of storage and perennation. Starch reserves in the cortical parenchyma enable the plant to survive extended periods of unfavorable conditions, including drought, cold, and substrate disturbance. The rhizome can regenerate new fronds even after complete defoliation, a capacity that contributes significantly to the species' resilience. The aromatic volatile compounds in the rhizome, primarily sesquiterpenes including germacrone, furanodienone, and related terpenoids, have been studied for their biological activity. Research has demonstrated antifungal, antibacterial, and insect-repellent properties of Phymatosorus rhizome extracts, suggesting these compounds serve a defensive function, protecting the fleshy, nutrient-rich rhizome from pathogens and herbivores. Photosynthesis follows the C3 pathway, with the coriaceous fronds showing efficient carbon fixation across a wide range of light intensities. The species maintains positive net photosynthesis at light levels as low as 15 micromoles per square meter per second, enabling growth in deep shade, while the thick cuticle and compact mesophyll structure protect against photodamage at higher light levels. Maximum photosynthetic rates occur at approximately 200 to 400 micromoles per square meter per second. The species demonstrates notable cold tolerance for a Polypodiaceae member, surviving temperatures several degrees below freezing in sheltered positions. This frost hardiness is associated with the accumulation of soluble sugars and proline in the frond tissue during autumn, compounds that function as cryoprotectants.

Spore Dispersal

Phymatosorus pustulatus produces spores abundantly on its prominently raised sori, which are among the most conspicuous in the Polypodiaceae. The pustulate elevation of the sori above the general frond surface enhances spore release by positioning the sporangia in the zone of maximum air turbulence along the frond surface. The spores are monolete, bilateral, approximately 42 to 58 micrometers in length, with a smooth to finely granulate perispore. The annulus mechanism drives dehiscence, and the relatively thick-walled sporangia may be particularly well suited to the temperate conditions of the New Zealand climate, where lower temperatures and higher humidity could otherwise impede the drying process necessary for spore release. The species' distribution across both North and South Islands of New Zealand, as well as its presence in southeastern Australia, demonstrates effective long-distance dispersal capacity. The Tasman Sea crossing between New Zealand and Australia, a distance of approximately 2,000 kilometers (1,240 miles), represents a significant dispersal barrier that the species has evidently overcome, though whether through a single event or multiple crossings is unknown. Spore germination is rapid under favorable conditions, occurring within one to three weeks at 55 to 72 °F (13–22 °C) on moist substrates. The gametophyte is bisexual and relatively robust for a fern prothallus, tolerating moderate environmental fluctuations. The species' readiness to colonize new substrates, including walls, garden features, and man-made structures, attests to effective spore dispersal within local environments.

Reproduction & Propagation

Phymatosorus pustulatus is among the easiest ferns to propagate, both from rhizome divisions and from spores. The thick, vigorous rhizome divides readily and divisions establish quickly, making this an ideal fern for sharing among gardeners. For division, cut sections of rhizome 8 to 15 centimeters (3–6 inches) long, each bearing at least one frond and roots. The robust rhizome tissue heals rapidly, but a dusting of cinnamon on cut surfaces provides additional protection. Pot divisions in standard growing mix or plant directly in the garden in sheltered positions. New growth appears within three to six weeks under favorable conditions. The species also self-propagates vegetatively by natural extension of the rhizome, and portions of rhizome that become detached from the parent plant through natural breakage often establish independently. This accounts for the readiness with which the species colonizes new substrates in gardens and urban environments. Spore propagation is straightforward. Collect ripe spores from mature sori and sow on moist sphagnum peat or a sterile soil surface. Maintain at 55 to 70 °F (13–21 °C) with consistent moisture. Germination occurs within two to four weeks, and the sporophyte stage is reached within four to eight months. Spore-grown plants develop the characteristic thick rhizome within their first year. In gardens, the species often naturalizes by self-sowing from spores, establishing on walls, rocks, and tree trunks without any intervention from the gardener.

Cultivation & Substrate

Phymatosorus pustulatus is one of the easiest ferns to cultivate, thriving in a range of conditions from cool, shaded positions to moderately bright, temperate environments. Its frost tolerance makes it one of the few epiphytic Polypodiaceae that can be grown outdoors year-round in cool temperate climates. For potting, use a rich, well-draining mix of equal parts peat or coco coir, bark, and perlite, optionally enriched with leaf mold. The thick rhizome should be positioned on the substrate surface, where it can extend freely. Shallow pots, wide troughs, or hanging baskets suit the creeping growth habit. Watering is straightforward: maintain consistent substrate moisture without waterlogging. The thick rhizome provides drought tolerance, and the species recovers well from temporary water stress, though prolonged drought causes frond dieback. Water with tap water; the species is not sensitive to mineral content. Light requirements are flexible, from deep shade to moderate bright indirect light (800–2,500 lux). The species tolerates lower light levels than most houseplants and is an excellent choice for dim indoor positions. Brighter conditions promote more divided frond forms. Temperature tolerance is exceptional for a Polypodiaceae member. The species thrives from 45 to 78 °F (7–26 °C) and tolerates brief exposures down to near-freezing. This makes it suitable for unheated conservatories, cool porches, and sheltered outdoor positions in zones as cold as 8a. Humidity of 50 to 80 percent is ideal, but the coriaceous fronds tolerate lower levels without significant damage. Fertilize monthly during the growing season with a standard balanced fertilizer at half strength.

Common Mistakes to Avoid

Overwatering in dense, poorly draining substrates is the most common error. Despite the species' moisture tolerance, a waterlogged substrate promotes rhizome rot. Use a well-draining mix and ensure containers have functional drainage holes. Placing the plant in full sun is a mistake. While P. pustulatus tolerates moderate light, direct sun, particularly afternoon sun, can scorch the fronds. Position in shade to bright indirect light. Keeping the plant in excessively warm conditions (above 82 °F / 28 °C for extended periods) can stress this temperate-adapted species. It performs best in cool to moderate temperatures and may languish in heated tropical environments. Mistaking the prominently raised sori for a disease or pest infestation is a surprisingly frequent mistake among growers unfamiliar with the species. The pustulate sori are the normal reproductive structures and a defining feature of the species. Neglecting the plant entirely because of its reputation for toughness can lead to gradually declining specimens. While resilient, P. pustulatus responds to regular care with more vigorous growth and better frond quality than a neglected plant. In garden settings, planting in exposed, windy positions subjects the thick but brittle fronds to mechanical damage. Provide shelter from strong winds.

Seasonal Considerations

In its native New Zealand, Phymatosorus pustulatus grows year-round but shows reduced activity during the cooler winter months. In Northern Hemisphere cultivation, this seasonal pattern is reversed. During spring, growth resumes vigorously with the production of new fronds from the advancing rhizome tip. Begin fertilization and increase watering. This is the optimal window for division and repotting. Summer growth is steady, and the plant benefits from consistent moisture and regular fertilization. In warm climates, provide afternoon shade and adequate ventilation. The species may slow growth during very warm periods but resumes when temperatures moderate. Autumn is a time of continued growth in mild conditions. Begin reducing fertilizer and allow the substrate to dry slightly more between waterings as growth slows. Winter is a period of reduced but not dormant activity for this cool-tolerant species. In outdoor cultivation in zones 8a–11, the plant typically maintains its fronds through winter unless severe frost causes temporary dieback. Indoor plants may produce occasional new fronds during winter in cool rooms. Cease fertilization and reduce watering. The species' frost tolerance means it can remain in unheated spaces that would be unsuitable for most other cultivated ferns. Resume full care protocols in early spring as new growth appears. In New Zealand, the species is effectively evergreen, maintaining fronds year-round in all but the coldest inland locations.

Diseases & Pests

Phymatosorus pustulatus is disease-resistant, a quality attributable in part to the antimicrobial terpenoid compounds present in its rhizome and, to a lesser extent, in its frond tissue. The species' robust constitution and broad environmental tolerance further reduce disease incidence. Rhizome rot can occur in waterlogged conditions, though the species is more resistant to this problem than many ferns due to its thick, well-protected rhizome tissue. If rot does develop, remove affected tissue and improve drainage. Fungal leaf spots (Cercospora, Phyllosticta) are uncommon but may occur on stressed fronds in excessively damp, poorly ventilated conditions. Remove affected fronds and improve air circulation. In New Zealand gardens, the species may be affected by fern scale (Pinnaspis aspidistrae), which can colonize the underside of fronds and the rhizome surface. Treat with horticultural oil spray. Slugs and snails can damage fronds, particularly young, tender growth; manage with iron phosphate baits or manual removal. Possums and other browsing animals may feed on the fronds in outdoor New Zealand gardens, but the plant's vigorous rhizome enables rapid recovery from browsing damage.

Indoor Growing & Terrariums

Phymatosorus pustulatus is an exceptionally adaptable indoor fern, tolerating the cool, variable conditions of typical temperate homes with ease. Its combination of attractive foliage, aromatic rhizome, and minimal care requirements makes it an ideal choice for both experienced fern growers and beginners. The species thrives in a wide range of indoor positions. Near north- or east-facing windows, on shelves and bookcases, in cool hallways, and even in garages and unheated conservatories, the hound's tongue fern maintains good health and appearance. Its tolerance of low light and cool temperatures sets it apart from most other indoor ferns, which typically demand warmer, brighter conditions. Display options include standard pots, hanging baskets, mounted on cork bark or driftwood, or grown in wide, shallow containers that showcase the creeping rhizome. The thick, scaled rhizome is ornamental in its own right and should be displayed rather than buried. As the rhizome extends and trails over container edges, it adds a naturalistic, organic quality to the display. Watering is infrequent compared to many ferns: allow the substrate surface to dry before watering, then water thoroughly. The species' drought tolerance means it survives forgotten watering sessions that would kill more demanding ferns. The aromatic quality of the rhizome adds a unique sensory dimension. During repotting or division, the sweet, spicy fragrance released by the disturbed rhizome is a delightful bonus appreciated by many growers. For a New Zealand-themed indoor plant collection, combine P. pustulatus with Asplenium bulbiferum, Blechnum species, and Cyathea dealbata for a display celebrating New Zealand's notable native fern flora.

Terrarium Setup

Phymatosorus pustulatus can be used in terrarium settings, though its vigorous growth and preference for cooler conditions make it best suited to large, cool terrariums rather than the small, warm enclosures typical of tropical setups. A terrarium of at least 40 liters (10 gallons) is recommended. Construct with a drainage layer, mesh separator, and rich substrate as described for other Phymatosorus species. The thick, creeping rhizome will readily colonize hardscape elements such as driftwood and cork bark, eventually creating a naturalistic display. Mount the rhizome on a prominent piece of hardscape to showcase its attractive scaled surface and allow room for extension. Provide LED lighting at 1,000 to 2,000 lux for 10 to 12 hours daily. Maintain temperatures below 78 °F (26 °C); cooler conditions of 55 to 70 °F (13–21 °C) are preferable. The enclosed environment maintains humidity above 75 percent. Ventilate frequently to prevent excessive heat buildup and stagnant air. The aromatic rhizome adds a pleasant fragrance when the terrarium is opened for maintenance. For a New Zealand-themed terrarium, combine P. pustulatus with other New Zealand natives such as small Asplenium species, Blechnum penna-marina, Selaginella, and miniature mosses to create a miniature representation of a New Zealand forest floor.

Landscape & Garden Use

Phymatosorus pustulatus 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

Phymatosorus pustulatus is abundant and widespread in New Zealand and is classified as Not Threatened in the New Zealand Threat Classification System. The species is common throughout both North and South Islands, occurring in both primary and secondary forests and readily colonizing urban environments. The species' ecological resilience, including its ability to grow in disturbed habitats and on man-made structures, provides strong protection against population decline. It is one of the few native ferns that has potentially benefited from human habitat modification, as the creation of gardens, walls, and other structures has provided additional colonization surfaces. In southeastern Australia, where the species also occurs, populations are less well studied but appear to be stable within their natural range. No conservation measures are currently required for this species.