Introduction & Discovery

Polypodium glycyrrhiza 'Longicaudatum' is a distinctive cultivar of the licorice fern, selected for its dramatically elongated pinnae that taper to remarkably long, attenuate, tail-like tips. The cultivar name Longicaudatum, from the Latin longus (long) and caudatus (tailed), precisely describes this defining characteristic, which gives each frond an elegant, almost feathery quality that sets it apart from the blunt-tipped or merely acute pinnae of the standard species. The parent species, Polypodium glycyrrhiza, is one of the most familiar and beloved ferns of the Pacific Northwest of North America, where it carpets the mossy trunks of bigleaf maples (Acer macrophyllum), red alders (Alnus rubra), and other trees in the temperate rainforests from southeastern Alaska to central California. The species name glycyrrhiza, meaning sweet root, refers to the distinctive licorice-like flavor of the rhizome, which has been used as a food flavoring and folk medicine by indigenous peoples of the Pacific Northwest for millennia. Like the wild species, 'Longicaudatum' follows a winter-green growth cycle, producing fresh fronds in autumn as the Pacific Northwest's rainy season begins and entering dormancy in late spring or early summer as conditions become warm and dry. This phenology is an adaptation to the pronounced wet-winter, dry-summer climate of the Pacific coastal region, where summer drought can be severe even in areas receiving abundant annual rainfall. For the fern enthusiast, 'Longicaudatum' offers a graceful enhancement of an already attractive species. The elongated, tail-like pinna tips create a softer, more flowing silhouette than the standard form, particularly appealing when the fronds are viewed in profile or when they sway gently in winter breezes. The cultivar is equally at home on mossy tree trunks, rocky banks, and in shaded garden beds, bringing the atmospheric beauty of the Pacific Northwest forest into the cultivated landscape.

Discovery & Naming

The cultivar 'Longicaudatum' was selected from cultivated or collected populations of Polypodium glycyrrhiza, identified by an observant grower who noticed the distinctively elongated pinna tips on one or more individuals and recognized the horticultural potential of this variation. The selection history is less extensively documented than that of the historic British Polypodium cultivars, but the cultivar has been recognized and distributed through specialist fern nurseries and pteridological societies. The parent species, Polypodium glycyrrhiza, was described by David Douglas, the Scottish botanical explorer who collected extensively in the Pacific Northwest in the 1820s and 1830s. Douglas noted the licorice-flavored rhizome and its use by indigenous peoples, leading to the choice of the specific epithet glycyrrhiza. The species has been in cultivation in European and North American gardens since the mid-nineteenth century. The recognition of P. glycyrrhiza as a species distinct from the European P. vulgare was based on morphological characters including the serrate pinna margins, the larger sori, and the distinctive rhizome flavor, subsequently confirmed by cytological and molecular evidence.

Frond Morphology

The fronds of Polypodium glycyrrhiza 'Longicaudatum' are pinnate, narrowly lanceolate in outline, typically 25 to 50 centimeters (10–20 inches) in total length, with a stipe of 8 to 18 centimeters (3–7 inches). The blade is 17 to 35 centimeters (7–14 inches) long and 6 to 14 centimeters (2.4–5.5 inches) wide, gradually tapering from the widest point at about one-third of the way from the base to a long, attenuate apex. The pinnae are the cultivar's distinguishing feature. They are narrowly triangular to linear-lanceolate, 3 to 8 centimeters (1.2–3 inches) long and 0.8 to 1.5 centimeters (0.3–0.6 inches) wide at the base, tapering gradually to remarkably long, attenuate tips that may extend 1 to 2 centimeters (0.4–0.8 inches) beyond where a standard P. glycyrrhiza pinna would end. These extended tips are the most reliable diagnostic feature of the cultivar, giving each pinna a graceful, tail-like appearance. Pinnae are attached to the rachis sessile or with a very short petiolule, alternate, spaced 1 to 2 centimeters apart. The margins are entire to finely serrate, a characteristic inherited from the parent species, which is distinguished from P. vulgare partly by its serrate pinna margins. The lamina is herbaceous, bright to medium green, thin-textured but not membranous. Venation is free, pinnately branched from the pinna costae, with veins forking once. Sori are round, large (2–3 millimeters diameter), exindusiate, arranged in a single row on each side of the pinna midvein, positioned between the midvein and the margin, typically four to eight sori per pinna. Mature sori are golden-orange. The rhizome is moderately thick, creeping, 4 to 7 millimeters in diameter, covered with golden-brown, lanceolate scales. The rhizome has a distinctive sweet, licorice-like flavor when tasted, a characteristic of the species.

Native Range & Distribution Map

Distribution map showing the native range of Polypodium glycyrrhiza 'Longicaudatum'.

Biology & Frond Morphology

Polypodium glycyrrhiza 'Longicaudatum' shares the fundamental biology of the parent species, including its characteristic winter-green phenology. The growth cycle is tightly synchronized with the Pacific Northwest's Mediterranean-type climate, though the species occurs in areas with one of the highest annual rainfall totals in North America. New fronds emerge in September to November as autumn rains begin, expanding rapidly from tightly coiled croziers at the rhizome apex. The elongated pinna tips of 'Longicaudatum' develop during the expansion phase, uncoiling to reveal their characteristic attenuate form. Fronds reach full size within three to five weeks and persist through winter into late spring. As summer approaches and conditions become warmer and drier, the fronds gradually senesce, beginning at the tips and margins and progressing inward. By mid-summer, the plant may be entirely deciduous, with only the dormant rhizome persisting. The licorice flavor of the rhizome is attributed to glycyrrhizin-like compounds, although the specific chemistry differs from true licorice (Glycyrrhiza glabra). The rhizome contains osladin, a steroidal saponin approximately 3,000 times sweeter than sucrose, which contributes the sweet taste. Additional compounds include various phenolics, flavonoids, and terpenoids. As a cultivar, 'Longicaudatum' is propagated vegetatively by rhizome division to maintain the elongated pinna morphology. The genetic basis of this trait is not fully characterized but appears to involve modifications in the timing and extent of apical growth in developing pinnae, resulting in an extended period of tip elongation that produces the characteristic attenuate form.

Spore Dispersal

Polypodium glycyrrhiza 'Longicaudatum' produces viable spores on its golden-orange sori, which mature during the winter growing season. Spore release occurs primarily during dry periods in late winter and early spring, when reduced humidity facilitates sporangial dehiscence through the annulus mechanism. The spores are monolete, bilateral, approximately 48 to 62 micrometers in length, with a verrucate to echinate perispore. Dispersal is primarily by wind, with the vast majority of spores deposited within meters of the parent plant but a small fraction carried over greater distances by atmospheric turbulence. In the Pacific Northwest, the primary colonization substrates for wild P. glycyrrhiza are the mossy surfaces of deciduous tree trunks and branches, particularly bigleaf maple. Spore germination requires consistently moist conditions and moderate temperatures (50–68 °F / 10–20 °C), conditions that are reliably present in the Pacific Northwest during the autumn and winter months when the moss-covered bark is saturated with rainfall. Spore-grown offspring of 'Longicaudatum' would not reliably reproduce the elongated pinna morphology, as the trait is likely polygenic and would segregate in sexual reproduction. However, some offspring may show partial expression of the trait, and growers interested in selecting new variants could use spore culture as a starting point.

Reproduction & Propagation

Rhizome division is the standard method for propagating 'Longicaudatum', ensuring that the elongated pinna morphology is faithfully reproduced. Divide in early autumn as new growth begins, or in late winter during the active growing season. Carefully detach sections of rhizome 5 to 10 centimeters (2–4 inches) long, each bearing at least one frond and associated roots. For epiphytic establishment, secure the division against a moss-covered tree trunk or log with cotton thread and a sphagnum pad. For terrestrial planting, set the rhizome on the substrate surface with roots in contact with the soil. Divisions establish rapidly in the cool, moist conditions of the autumn growing season. New roots develop within two to four weeks, and additional fronds may emerge within the same growing season. Spore propagation produces variable offspring. Sow spores on acidic, sterilized growing medium at 55 to 65 °F (13–18 °C). Gametophytes develop within three to six weeks and sporophytes within four to eight months. Select from the resulting population for any individuals showing the elongated pinna trait. Natural detachment and reestablishment of rhizome fragments is a common mode of vegetative spread in the wild, and fragments of 'Longicaudatum' rhizome placed on suitable substrates often establish without special treatment.

Cultivation & Substrate

Polypodium glycyrrhiza 'Longicaudatum' is cultivated in the same manner as the wild species, with attention to the summer-dormant, winter-green growth cycle. The cultivar performs best in climates that approximate the Pacific Northwest's wet winters and dry summers, though it adapts to a range of temperate conditions. The ideal planting position is on a mossy tree trunk, log, or rock face in a shaded woodland setting. To establish the fern on a tree, secure rhizome divisions in a pad of moist sphagnum moss against the bark surface, holding them in place with cotton twine or mesh netting. The rhizome will root into the moss and bark within one growing season. This epiphytic display is the most naturalistic and aesthetically rewarding way to grow the species. For ground-level planting, provide acidic to neutral, humus-rich, well-drained soil in partial to full shade. Incorporate leaf mold, bark, and coarse grit to ensure the excellent drainage that the species requires, particularly during the summer dormancy period when a wet substrate can rot the resting rhizome. No supplemental watering is needed during the winter growing season in typical Pacific Northwest conditions. In drier climates, occasional watering during prolonged dry autumn or winter periods maintains frond quality. During summer dormancy, allow the site to dry naturally; the dormant rhizome requires no attention. Fertilization is minimal. An annual mulch of leaf mold in autumn provides sufficient nutrition. The species is fully hardy to zone 6a and requires no winter protection.

Common Mistakes to Avoid

Overwatering during summer dormancy is the most serious cultivation error, potentially rotting the resting rhizome. Once the fronds have senesced in late spring, cease watering and allow the site to dry naturally. Planting in alkaline soil is a mistake. Unlike P. cambricum, the licorice fern prefers acidic to neutral substrates. Avoid lime-enriched soils and calcareous rock. Assuming the plant has died during summer dormancy is a common misconception. The bare rhizome will produce fresh fronds in autumn, and the summer rest period is a natural part of the growth cycle. Planting in exposed, sunny positions damages the thin-textured fronds and prevents proper development of the elongated pinna tips. Provide shade and shelter from wind. Expecting 'Longicaudatum' to grow in warm, humid conditions year-round misunderstands the species' biology. The winter-green cycle requires a period of summer warmth and dryness followed by cool, moist autumn and winter conditions. Ignoring the epiphytic potential of this fern is a missed opportunity. Growing 'Longicaudatum' on a mossy tree trunk or log produces the most attractive and naturalistic display.

Seasonal Considerations

The seasonal care cycle for 'Longicaudatum' mirrors that of wild Polypodium glycyrrhiza in the Pacific Northwest. Autumn (September–November): New croziers emerge from the rhizome. If the plant is grown in the ground or in a container, ensure the substrate is moist. Epiphytic specimens benefit from the natural increase in rainfall and humidity. Apply a light mulch of leaf mold. Winter (December–February): Fronds are at their peak, the elongated pinna tips creating an elegant winter display. No special care is needed. The fronds are frost-hardy and tolerate snow cover. Spring (March–May): Fronds continue to photosynthesize and sori mature. As temperatures rise and days lengthen, fronds gradually begin to senesce from the tips downward. Allow natural senescence to proceed; the dying fronds return nutrients to the rhizome. Late spring to summer (May–August): Fronds die back completely and the plant enters dormancy. Remove dead frond material for tidiness if desired. Cease watering and allow the site to dry. The rhizome rests through the warm, dry summer months. Late summer (August–September): Watch for the first signs of new crozier emergence, signaling the return to active growth. Resume gentle watering if conditions have been particularly dry.

Diseases & Pests

Polypodium glycyrrhiza 'Longicaudatum' is generally healthy and disease-resistant. The principal disease risk is rhizome rot during summer dormancy if the substrate remains excessively wet. Ensuring good drainage at the planting site and avoiding summer irrigation prevents this problem. Fungal leaf spots may occur during prolonged wet periods in winter, typically caused by Cercospora or related fungi. These are rarely serious and usually require no treatment beyond removing heavily affected fronds. Slug and snail damage is the most common pest problem, particularly during the soft, vulnerable crozier stage in autumn. Protect emerging fronds with barriers or iron phosphate baits. In the Pacific Northwest, the species may occasionally be affected by the fern midge (Dasineura filicina), whose larvae cause galling of frond tissue. Affected fronds should be removed and destroyed to reduce local midge populations. No serious or persistent disease problems are recorded for this species in garden cultivation.

Indoor Growing & Terrariums

Polypodium glycyrrhiza 'Longicaudatum' is not well suited to typical indoor cultivation in heated homes. The species requires cool temperatures, excellent air circulation, and a summer dormancy period that heated, stable indoor environments do not provide. In cool, unheated rooms, enclosed porches, or conservatories where winter temperatures remain between 35 and 60 °F (2–16 °C), the fern can be grown in containers during its active season. Use a well-drained, acidic potting mix and place near a window with good indirect light. The elongated pinna tips of 'Longicaudatum' are particularly attractive in container culture, where the fronds can arch gracefully over the container edge. A shallow dish or trough planted with the fern and a carpet of moss creates a miniature representation of the Pacific Northwest forest floor. During summer dormancy, move the container to a cool, dry location such as a garage or shed. Resume watering in early autumn when new croziers appear. For growers in the Pacific Northwest, the species is far more rewarding grown outdoors or on a sheltered porch than in a heated indoor space.

Terrarium Setup

Polypodium glycyrrhiza 'Longicaudatum' is not a conventional terrarium fern due to its summer dormancy requirement and preference for cool temperatures. However, it can be displayed in a cool, temperate terrarium or glass case during its active growing season (autumn through spring). Use a well-drained, acidic substrate incorporating leaf mold, pine bark fines, and perlite. Mount the rhizome on a piece of mossy driftwood or cork bark for the most naturalistic display. Maintain cool temperatures of 40 to 60 °F (5–16 °C) with LED lighting at 2,000 to 3,000 lux for 8 to 10 hours daily. The elongated pinna tips of 'Longicaudatum' are best appreciated in the close-up viewing afforded by a terrarium setting, where the graceful taper of each pinna can be observed in detail. During summer, remove the rhizome from the terrarium and store in a cool, dry location until autumn, or reduce lighting and watering to simulate natural dormancy conditions. Companion species for a Pacific Northwest temperate terrarium include Blechnum spicant (deer fern), Selaginella oregana, and native mosses such as Leucolepis.

Landscape & Garden Use

Polypodium glycyrrhiza 'Longicaudatum' 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

The parent species, Polypodium glycyrrhiza, is widespread and abundant throughout its range in the Pacific Northwest and is not considered threatened. It is common in both protected and unprotected habitats and readily colonizes urban trees and structures. Climate change may affect the species' distribution, particularly in the southern portion of its range (California), where increasing drought severity and duration could stress populations. However, in the core of its range (British Columbia, Washington, Oregon), the species is likely to remain common. The cultivar 'Longicaudatum' exists only in cultivation and depends on the continued interest of fern growers for its perpetuation. It is maintained by specialist nurseries and pteridological societies.