Hymenophyllaceae

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

See text

The Hymenophyllaceae (filmy ferns and bristle ferns) is a family of two or more genera[1] 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.[2]

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[3]

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.[3] This system has thus far shown some acceptance.[1] The genera and subgenera assigned by this system are:

References

  1. 1 2 Christenhusz et al.: A linear sequence of extant families and genera of lycophytes and ferns Phytotaxa 19: 7-54. (18 Feb. 2011)
  2. ↑ A filmy fern from the Upper Triassic of North Carolina (USA) - Axsmith et al. 88 (9): 1558 - American Journal of Botany
  3. 1 2 Ebihara et al.: A Taxonomic Revision of Hymenophyllaceae Blumea - Biodiversity, Evolution and Biogeography of Plants, Volume 51, Number 2, July 2006 , pp. 221-280(60)
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