Hymenophyllaceae

Hymenophyllaceae
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Hymenophyllum tunbrigense in Luxembourg
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Polypodiopsida /  Pteridopsida (disputed)
Order:	Hymenophyllales
Family:	Hymenophyllaceae Link
Genera
See text

The Hymenophyllaceae (filmy ferns and bristle ferns) is a family of two or more genera and over 600 species of ferns, with a subcosmopolitan distribution, but generally restricted to very damp places or to locations where they are wetted by spray from waterfalls or springs. A recent fossil find shows that ferns of Hymenophyllaceae have existed since at least the Upper Triassic.

The great majority of the species are found in tropical rainforests, but some also occur in temperate rainforests (particularly New Zealand, with 25 species) and slightly drier forest regions. In Europe they are restricted to the Atlantic Ocean fringes of the continent, notably in the Azores, Ireland, and western Great Britain, but one species (Hymenophyllum tunbrigense) locally east to Luxembourg, another (H. wilsonii) so far north as West Norway, Faeroes and South Iceland, while in North America, they are restricted to the humid eastern third of the continent.

They often appear as very dark green or even black clumps and may be mistaken for a robust moss or liverwort. The stem is thin and wiry and the fronds variously pinnate with a single strand ("nerve") of vascular tissue. In most species, the frond, apart from the vascular tissue, is only a single cell thickness, and they do not have any stomata; this makes the plants very susceptible to desiccation where a reliable water supply is not present. The sori are borne at the leaf margins at the end of the nerve. Individual plants may persist for many years.

Genera

Hymenophyllaceae

Hymenophyllum  Crepidomanes  Vandenboschia  Didymaglossum  Polyphlebium  Callistopteris  Trichomanes  Abrodictyum  Cephalomanes

Phylogram of Hymenophyllaceae genera

Traditionally, only two genera of Hymenophyllaceae have been recognized: (1) Hymenophyllum with bivalved involucres, and (2) Trichomanes with tubular involucres. Subsequent proposals have created 34 genera (Copeland 1938), 6 genera (Morton 1968), 47 genera (Sermolli 1977), and 8 genera (Iwatsuki 1984). But these classifications have all had only limited regional acceptance. Recent molecular phylogenic studies do show two distinct monophyletic clades of fairly equal size, but they are only roughly aligned with the two traditional genera. For example. the traditional Trichomanes subtaxa Pleuromanes and Cardiomanes were shown to belong to the "hymenophylloid" clade. To reflect these recent discoveries Atsushi Ebihara and Kunio Iwatsuki, in 2006, revised the taxonomy of Hymenophyllaceae to place all species of the "hymenophylloid" clade in a single Hymenophyllum genus, and to place the eight clear "trichomanoid" subclades in eight corresponding genera. This system has thus far shown some acceptance. The genera and subgenera assigned by this system are:

• The "hymenophylloid" clade:
  • Hymenophyllum Sm. 1793 – about 250 species
    • subg. Hymenophyllum – about 100 species
    • subg. Sphaerocionium (C.Presl) C.Chr. 1934 – about 70 species
    • subg. Mecodium C.Presl ex Copel. 1937 – more than 35 species
    • subg. Globosa (Prantl) Ebihara & K.Iwats. 2006 – about 25 species
    • subg. Pleuromanes (C.Presl) Ebihara & K.Iwats. 2006 – 5 species
    • subg. Myrmecostylum (C.Presl) Ebihara & K. Iwats. 2006 – at least 8 species
    • subg. Hymenoglossum (C.Presl) R.M.Tryon & A.F.Tryon 1981 – at least 3 species
    • subg. Fuciformia Ebihara & K.Iwats. 2006 – 2 species
    • subg. Diploöphyllum (Bosch) Ebihara & K.Iwats. 2006 – 1 species
    • subg. Cardiomanes (C. Presl) Ebihara & K.Iwats. 2006 – 1 species

• The "trichomanoid" clade:
  • Didymoglossum Desv. 1827 – more than 30 species
    • subg. Didymoglossum – more than 20 species
    • subg. Microgonium (C.Presl) Ebihara & K.Iwats. 2006 – more than 10 species
  • Crepidomanes (C.Presl) C.Presl 1849 – more than 30 species
    • subg. Crepidomanes
    • subg. Nesopteris (Copel.) Ebihara & K.Iwats. 2006
  • Polyphlebium Copel. 1938 – about 15 species
  • Vandenboschia Copel. 1938 – more than 15 species
    • subg. Vandenboschia – more than 15 species
    • subg. Lacosteopsis (Prantl) Ebihara & K.Iwats. 2006 – at least 2 species
  • Abrodictyum C.Presl 1843 – about 25 species
    • subg. Abrodictyum – about 15 species
    • subg. Pachychaetum (C.Presl) Ebihara & K.Iwats. 2006 – more than 10 species
  • Trichomanes L. 1753 – more than 60 species
    • subg. Trichomanes – more than 30 species
    • subg. Feea (Bory) Hook. 1844 – more than 5 species
    • subg. Davalliopsis (Bosch) Ebihara & K.Iwats. 2006 – at least 1 species
    • subg. Lacostea (Bosch) C. Chr. 1906 – more than 4 species
  • Cephalomanes C.Presl 1843 – about 4 species
  • Callistopteris Copel. 1938 – about 5 species

References

• Germplasm Resources Information Network: Hymenophyllaceae
• Flora of New Zealand (2004): Hymenophyllaceae
• USDA Plants Profile: Distribution in U.S.A.
• E.B.Copeland. 1947. Genera Filicum. Waltham.
• C.Michael Hogan. 2010. Fern. Encyclopedia of Earth. eds. Saikat Basu and C.Cleveland. National Council for Science and the Environment. Washington DC.
• H.A.Hyde, A.E.Wade, & S.G.Harrison. 1978. Welsh Ferns. National Museum of Wales. ISBN 0-7200-0210-9.
• Ebihara, Atsushi; Dubuisson, Jean-Yves; Iwatsuki, Kunio; Hennequin, Sabine; Ito, Motomi: A Taxonomic Revision of Hymenophyllaceae. Blumea 51:2,2006, pp. 221–280 [1]