Asplenium scolopendrium

The most striking and unusual feature of the fern is its simple, strap-shaped undivided fronds. The leaves' supposed resemblance to the tongue of a hart (an archaic term for a male red deer) gave rise to the common name "hart's-tongue fern".

Linnaeus first gave the hart's-tongue fern the binomial Asplenium scolopendrium in his Species Plantarum of 1753.[4] The Latin specific epithet scolopendrium is derived from the Greek skolopendra, meaning a centipede or millipede; this is due to the sori pattern being reminiscent of a myriapod's legs.[5][6]

A global phylogeny of Asplenium published in 2020 divided the genus into eleven clades,[7] which were given informal names pending further taxonomic study. A. scolopendrium belongs to the "Phyllitis subclade" of the "Phyllitis clade".[8] Members of the Phyllitis clade have undivided or pinnatifid leaf blades with a thick, leathery texture, persistent scales on their stalk, and often possess anastomosing veins. Members of the Phyllitis subclade have undivided leaves with freely branching veins and single or paired sori. They are widely distributed through the Northern Hemisphere.[9] Its closest relative within the subclade is A. komarovii, with which it forms a clade (the former segregate genus Phyllitis), sister to A. sagittatum.[8]

One variety and two subspecies are currently accepted:[10]

• A. scolopendrium subsp. scolopendrium, is native to Europe and North Africa;
• A. scolopendrium var. americanum, is native to the United States, Mexico and Ontario in Canada;
• A. scolopendrium subsp. antri-jovis, is native to Greece, Crete and Turkey.

Morphological differences between the varieties are minor, but the North American variety americanum is tetraploid, while the Old World subspecies A. scolopendrium scolopendrium) is diploid.[11]

Asplenium scolopendrium is a common species in the Old World:

• The subspecies scolopendrium occurs throughout Europe (including the Caucasus and the British Isles), the Middle East, and North Africa (in Morocco, Algeria, Tunisia and Libya, as well as the Canary Islands). It has also been introduced to the Falkland Islands. A. scolopendrium var. scolopendrium is rarely found in North America. Unlike its American counterpart, the scolopendrium of Europe is used for many horticultural uses. [12] [13] Specimens of this variety found in North America (such as in New Brunswick and Ontario in Canada, and Maryland in the United States) are considered naturalized descendants of cultivated plants.[14]

In North America, it occurs in rare, widely scattered populations located in different locales:

• in the Mexican states of Chiapas, Coahuila, Nuevo León, and Oaxaca, as well as the Caribbean island of Hispaniola (in Haiti).[15]
• along the Onondaga Limestone and Niagara Escarpment geological formations in Central New York (present in 2 counties), southern Ontario (present in 7 counties), and the eastern Upper Peninsula in Michigan (present in 2 counties). Exceptions are disjunct populations that exist in Alabama (in Fern Cave National Wildlife Refuge, a wildlife refuge centered around an off-limits cave in Jackson County, Alabama, where it has declined heavily due to illegal plant collecting, and an undisclosed pit in Morgan County that is also off-limits and protected), and Tennessee (in just a single county); these southern populations are at dire risk of extirpation.[16][17] An introduced population descended from New York plants is found in New Jersey; it is a remnant of a 1936 effort to practice ex-situ conservation of populations in New York.[18]
• In 2020, a new population of hart's-tongue ferns was discovered inside a cave with basaltic lava flows in El Malpais National Monument, Cibola County, New Mexico; this represents the first confirmed population of the species in North America west of the Mississippi. Genetic analyses and surveys are currently being performed to determine the population's variation and overall health. [19]

The unique dispersal of Asplenium scolopendrium has caught the attention of international botanists. In fact, the very existence of such varieties beg that "...these populations arose following colonization events involving a single spore".[20]

The plants grow on neutral, calcium-rich, and/or lime-rich substrates under deciduous hardwood canopies (usually sugar maples in eastern North America), including moist soil and damp crevices in old walls; they are found most commonly in shaded areas. Plants in full sun are usually stunted and yellowish in colour, while those in full shade are dark green and healthy. The disjunct populations of the North American variation in the southeastern US are found exclusively in sinkhole pits or limestone caves.[21] These populations may be relics of cooler Pleistocene climates.[17]

• 
  Habitat
• 
  A cultivar with frilled frond margins.
• 
  A specimen growing in lime mortar on a wall.
• 
  Example of the North American variety.

• Linnaeus, C. (1753). Species Plantarum. Vol. II (1st ed.). Stockholm: Laurentii Salvii.
• Xu, Ke-Wang; Zhang, Liang; Rothfels, Carl J.; Smith, Alan R.; Viane, Ronald; Lorence, David; Wood, Kenneth R.; Cheng, Cheng-Wei; Knapp, Ralf; Zhou, Lin; Lu, Ngan Thi; Zhou, Xin-Mao; Wei, Hong-Jin; Fan, Qiang; Chen, Su-Fang; Cicuzza, Daniele; Gao, Xin-Fen; Li, Wen-Bo; Zhang, Li-Bing (2020). "A global plastid phylogeny of the fern genus Asplenium (Aspleniaceae)". Cladistics. 36 (1): 22–71. doi:10.1111/cla.12384. PMID 34618950. S2CID 201197385.

• Hyde, H. A., Wade, A. E., & Harrison, S. G. (1978). Welsh Ferns. National Museum of Wales. ISBN 0-7200-0210-9.
• Parker, Rosemarie (December 2009). "A Real Rarity". Finger Lakes Native Plant Society. A popular article on hart's tongue fern that includes several references and a discussion of cultivation possibilities for the European and American varieties. The article strongly discourages collection and or cultivation of the North American variety.

Wikimedia Commons has media related to Asplenium scolopendrium.

• Commentary and video on Hart's Tongue ferns at Lynn Glen, Dalry, Scotland