Hart's-Tongue Fern

Asplenium scolopendrium has a broad distribution across the Northern Hemisphere, occurring naturally in Europe, North Africa, parts of western and central Asia, and eastern North America.

• In Europe, it ranges from the British Isles and Scandinavia south to the Mediterranean and the Caucasus
• In North America, it is found primarily in the eastern United States and southern Ontario, with disjunct populations in the Ozark region
• The species is considered a glacial relict in parts of its range, having retreated to sheltered limestone refugia during the last Ice Age
• The genus Asplenium has a fossil record extending to the Eocene (~50 million years ago), though fossil evidence specific to A. scolopendrium is limited
• The species name "scolopendrium" derives from the Greek "skolopendra" (centipede), referring to the linear arrangement of sori on the underside of fronds, which resembles the legs of a centipede

The Hart's-Tongue Fern is a perennial evergreen fern typically growing 20 to 60 cm tall, with a distinctive morphology that sets it apart from most other ferns.

Rhizome & Stipes:
• Rhizome is short, erect to ascending, covered with dark brown, lanceolate scales
• Stipes are short (typically 2–10 cm), dark brown to purplish-brown at the base, green toward the blade
• Stipe scales are narrowly lanceolate with entire margins

Fronds:
• Simple, undivided, strap-shaped to narrowly lanceolate — unique among European ferns
• Typically 20–60 cm long and 3–6 cm wide, with a heart-shaped (cordate) base and a pointed apex
• Texture is leathery to somewhat fleshy; bright glossy green on the upper surface
• Margins are typically entire (smooth), though cultivated varieties may be wavy, crisped, or forked
• A prominent, raised midrib (costa) runs the full length of the frond

Sori:
• Arranged in a distinctive herringbone pattern on the underside of the fronds
• Sori are linear, elongated, and borne in pairs on either side of the secondary veins
• Each sorus is covered by a thin, whitish to pale brown indusium
• The centipede-like arrangement of sori is the origin of the species epithet "scolopendrium"
• Spores are monolete, yellowish-brown, and released in late summer to autumn

The Hart's-Tongue Fern is strongly associated with calcareous (lime-rich) substrates and shaded, humid microclimates.

• Frequently found on limestone cliffs, cave entrances, mortared walls, and rocky ravines
• Thrives in deep shade to semi-shade, often in the understory of deciduous woodlands
• Prefers well-drained but consistently moist conditions; intolerant of prolonged drought
• Commonly grows in association with mosses and liverworts on rock surfaces and old walls
• Tolerant of relatively low light levels, making it one of the few ferns capable of persisting in deeply shaded limestone crevices

Humidity Requirements:
• Prefers moderate to high atmospheric humidity but is more tolerant of dry air than many other ferns
• Can survive in relatively dry microhabitats if soil moisture is adequate

Reproduction:
• Spores are wind-dispersed and require moist, shaded conditions to germinate
• Gametophyte stage requires a film of water for sperm to swim to the archegonium
• Vegetative reproduction through bulbils is not typical, though some cultivated forms produce plantlets at frond tips

The conservation status of Asplenium scolopendrium varies across its range:

• Globally assessed as Least Concern (LC) by the IUCN due to its wide distribution and stable overall population
• In the United Kingdom, it is widespread but has experienced local declines due to habitat loss and over-collection
• In parts of eastern North America, disjunct populations (particularly in the Ozarks and southern Appalachians) are considered rare and are monitored by state heritage programs
• Threats include quarrying of limestone habitats, removal from old walls during renovation, and illegal collection for horticulture
• The species is listed under Appendix II of the Bern Convention in Europe, affording it legal protection in signatory countries
• Several cultivated varieties are maintained in botanical garden collections as a conservation measure

The Hart's-Tongue Fern is a popular ornamental fern for shade gardens, rockeries, and container cultivation, prized for its architectural fronds and year-round evergreen foliage.

Light:
• Prefers deep shade to semi-shade; tolerates more shade than most ferns
• Avoid direct sunlight, which can scorch the fronds

Soil:
• Requires alkaline to neutral soil (pH 6.5–8.0); strongly calcicole
• Well-drained but moisture-retentive; a mix of leaf mold, grit, and crushed limestone is ideal
• Tolerates thin soils over rock and can grow in mortar joints of old walls

Watering:
• Keep soil consistently moist during the growing season
• More drought-tolerant than many ferns once established, but prolonged dry periods cause frond browning
• Avoid waterlogging, which can lead to rhizome rot

Temperature:
• Hardy in USDA zones 4–9 (approximately -34°C to -1°C minimum)
• Evergreen in mild climates; fronds may become tattered in harsh winters but recover in spring
• Optimal growth temperature: 10–20°C

Propagation:
• Spore sowing is the primary method; spores germinate in 2–6 weeks under humid, warm conditions
• Division of established clumps in early spring is possible but the plant resents root disturbance
• Some cultivars produce bulbils at frond tips, which can be pegged down to soil to root

Common Problems:
• Frond browning → insufficient moisture or excessive sun exposure
• Slugs and snails → can cause significant damage to young fronds
• Scale insects → occasionally infest the midrib on the underside of fronds
• Frond tattering in winter → cosmetic; new fronds unfurl in spring