{{Short description|Family of ferns}} {{Automatic taxobox | fossil_range = {{fossil range|Upper Triassic|Recent}} | image = WP-Hymenophyllum-Exkursion nach Berdorf (Luxemburgexkursion) 011.jpg | image_caption = ''Hymenophyllum tunbrigense'' in Luxembourg | display_parents = 2 | parent_authority = A.B.Frank | taxon = Hymenophyllaceae | authority = Link | subdivision_ranks = Genera | subdivision = See text }}
The '''Hymenophyllaceae''', the '''filmy ferns''' and '''bristle ferns''', are a family of two to nine genera (depending on classification system) and about 650 known species<ref name="Christenhusz-Byng2016">{{cite journal |author1=Christenhusz, M. J. M. |author2=Byng, J. W. | year = 2016 | title = The number of known plants species in the world and its annual increase | journal = Phytotaxa | volume = 261 | pages = 201–217 | url = http://biotaxa.org/Phytotaxa/article/download/phytotaxa.261.3.1/20598 | doi = 10.11646/phytotaxa.261.3.1 | issue = 3 | publisher = Magnolia Press |bibcode=2016Phytx.261..201C | doi-access = free }}</ref> 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. Fossil evidence shows that ferns of the family Hymenophyllaceae have existed since at least the Upper Triassic.<ref>[https://bsapubs.onlinelibrary.wiley.com/doi/pdfdirect/10.2307/3558399 A filmy fern from the Upper Triassic of North Carolina (USA) - Axsmith et al. 88 (9): 1558 - American Journal of Botany<!-- Bot generated title -->]</ref>
==Description== They often appear as very dark green or even black clumps and may be mistaken for a robust moss or liverwort. The rhizome is usually thin and wiry and the fronds variously pinnate with a single strand ("nerve") of vascular tissue. As in most ferns, young fronds have circinate vernation. In most species, the frond, apart from the vascular tissue, is only a single cell thick, and they do not have any stomata. The cuticle is also greatly reduced or absent,<ref name="smith-etal-2006">{{cite journal |last1=Smith |first1=Alan R. |last2=Pryer |first2=Kathleen M. |last3=Schuettpelz |first3=Eric |last4=Korall |first4=Petra |last5=Schneider |first5=Harald |last6=Wolf |first6=Paul G. |title=A classification for extant ferns |journal=Taxon |volume=55 |issue=3 |date=August 2006 |pages=705–731 |doi=10.2307/25065646 |url=https://www.fieldmuseum.org/sites/default/files/smith-et-al-taxon-2006.original.pdf |jstor=25065646 |bibcode=2006Taxon..55..705S |access-date=2016-12-22 |archive-date=2021-12-09 |archive-url=https://web.archive.org/web/20211209070955/https://www.fieldmuseum.org/sites/default/files/smith-et-al-taxon-2006.original.pdf }}</ref> leaving filmy ferns poikilohydric and very susceptible to desiccation where a reliable water supply is not present.<ref>{{cite journal | last1=Proctor | first1=M. C. | title=Light and desiccation responses of some Hymenophyllaceae (filmy ferns) from Trinidad, Venezuela and New Zealand: Poikilohydry in a light-limited but low evaporation ecological niche | journal=Annals of Botany | date=2012 | volume=109 | issue=5 | pages=1019–1026 | doi=10.1093/aob/mcs012 | pmid=22334496 | pmc=3310494 }}</ref> The leaves occasionally bear hairs, but scales are generally not present.<ref name="smith-etal-2006" /> The sori are borne at the leaf margins<ref name="smith-etal-2006" /> at the end of the nerve. They are protected by conical, bivalvate, or tubular indusia. Within the sori, sporangia mature starting at the apex of the sorus and progressing to the base. They have a continuous, oblique annulus and release round, green trilete spores. The spores grow into thread- or ribbon-like gametophytes; in many species, the gametophyte has an extended, independent lifespan and can reproduce asexually by fragmenting or releasing gemmae.<ref name="smith-etal-2006" />
Individual plants may persist for many years.
==Taxonomy== In the molecular phylogenetic classification of Smith et al. in 2006, the Hymenophyllales, containing the single family Hymenophyllaceae, were placed in class Polypodiopsida ''sensu stricto'' (the leptosporangiate ferns).<ref name="smith-etal-2006" /> The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009)<ref name="christenhusz-etal-2011">{{cite journal |first1=Maarten J. M. |last1=Christenhusz |author-link1=Maarten J. M. Christenhusz |first2=Xian-Chun |last2=Zhang |first3=Harald |last3=Schneider |date=18 February 2011 |title=A linear sequence of extant families and genera of lycophytes and ferns |journal=Phytotaxa |volume=19 |pages=7–54 |url=http://www.mapress.com/phytotaxa/content/2011/f/pt00019p054.pdf |doi=10.11646/phytotaxa.19.1.2 |bibcode=2011Phytx..19....7C }}</ref> which placed all land plants in Equisetopsida,<ref>{{cite journal |last1=Chase |first1=Mark W. |author-link1=Mark Wayne Chase |last2=Reveal |first2=James L. |author-link2=James L. Reveal |title=A phylogenetic classification of the land plants to accompany APG III |journal=Botanical Journal of the Linnean Society |volume=161 |issue=2 |pages=122–127 |date=October 2009 |doi=10.1111/j.1095-8339.2009.01002.x|doi-access=free }}</ref> reclassified Smith's Polypodiopsida as subclass Polypodiidae and placed the Hymenophyllales there. The circumscription of the order and its families was not changed,<ref name="christenhusz-etal-2011" /> and that circumscription and placement in Polypodiidae has subsequently been followed in the classifications of Christenhusz and Chase (2014)<ref name="christenhusz-chase-2014">{{cite journal |last1=Christenhusz |first1=Maarten J. M. |last2=Chase |first2=Mark W. |title=Trends and concepts in fern classification |journal=Annals of Botany |volume=113 |issue=4 |date=13 February 2014 |pages=571–594 |doi=10.1093/aob/mct299|pmid=24532607 |pmc=3936591 }}</ref> and PPG I (2016).<ref name="PPGI">{{cite journal |author=The Pteridophyte Phylogeny Group |title=A community-derived classification for extant lycophytes and ferns |journal=Journal of Systematics and Evolution |volume=54 |issue=6 |pages=563–603 |date=November 2016 |doi=10.1111/jse.12229|bibcode=2016JSyEv..54..563. |s2cid=39980610 |doi-access=free }}</ref>
The division of the family into genera was disputed, {{As of|lc=yes|2019|October}}. Traditionally, only two genera of Hymenophyllaceae have been recognized: (1) ''Hymenophyllum'' with bivalved involucres, and (2) ''Trichomanes'' s.l. with tubular involucres. Subsequent proposals have created 34 genera (Copeland 1938), 6 genera (Morton 1968), 47 genera (Sermolli 1977), and 8 genera (Iwatsuki 1984). These classifications 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 genus ''Hymenophyllum'', and to place the eight clear "trichomanoid" subclades in eight corresponding genera.<ref name=ebi>{{cite journal |last1=Ebihara |first1=Atsushi |last2=Dubuisson |first2=Jean-Yves |last3=Iwatsuki |first3=Kunio |last4=Hennequin |first4=Sabine |last5=Ito |first5=Motomi |title=A Taxonomic Revision of Hymenophyllaceae |journal=Blumea |volume=51 |issue=2 |date=July 2006 |pages=221–280 |doi=10.3767/000651906x622210|bibcode=2006Blume..51..221E |url=http://www.repository.naturalis.nl/document/566095 }}</ref>
This subdivision was recognized by Smith et al. in 2006<ref name="smith-etal-2006" /> and Christenhusz et al. in 2011,<ref name="christenhusz-etal-2011" /> but Christenhusz and Chase, in 2014, reverted to combining the trichomanoid clades into ''Trichomanes''.<ref name="christenhusz-chase-2014" /> The PPG I classification of 2016 again recognizes the segregate genera (and treats the two clades as subfamilies, Hymenophylloideae and Trichomanoideae),<ref name="PPGI" /> although the segregate genera are not always accepted by contemporary floras; e.g., as of 2016, the ''Flora of New Zealand'' preferred to recognize ''Trichomanes'' s.l. due to the difficulty of morphologically distinguishing the segregate genera.<ref>{{cite web |title=Hymenophyllaceae Mart. |publisher=Flora of New Zealand |url=http://www.nzflora.info/factsheet/Taxon/Hymenophyllaceae.html |access-date=22 December 2016}}</ref>
===Genera=== The genera used in PPG I and the subgenera assigned by the system of Ebihara et al. are:
{{cladogram |title=Phylogeny of Hymenophyllaceae<ref name=ebi/> |cladogram= {{clade| style=font-size:90%;width:300px |1={{clade |label1=Hymenophylloideae |1=''Hymenophyllum'' |label2=Trichomanoideae |2={{clade |1={{clade |1=''Abrodictyum'' |2=''Cephalomanes'' }} |2={{Clade |1=''Trichomanes'' s.s. |2={{clade |1=''Callistopteris'' |2={{clade |1=''Polyphlebium'' |2={{clade |1=''Didymoglossum'' |2={{clade |1=''Crepidomanes'' |2=''Vandenboschia'' }} }} }} }} }} }} }} }} }} {{cladogram |title=Phylogeny of Hymenophyllaceae<ref>{{cite journal |last1=Nitta |first1=Joel H. |last2=Schuettpelz |first2=Eric |last3=Ramírez-Barahona |first3=Santiago |last4=Iwasaki |first4=Wataru |display-authors=et al. |year=2022 |title=An Open and Continuously Updated Fern Tree of Life |journal=Frontiers in Plant Science |volume=13 |issue= |article-number= 909768| doi=10.3389/fpls.2022.909768 |pmid= 36092417|pmc= 9449725|bibcode= 2022FrPS...1309768N|doi-access=free}}</ref><ref>{{cite web|last1= |first1= |last2= |display-authors=et al. |year=2024 |title=Tree viewer: interactive visualization of FTOL |url=https://fernphy.github.io/viewer.html |version=FTOL v1.7.0 (GenBank release 261) |access-date=1 May 2025}}</ref> |cladogram= {{clade| style=font-size:90%;width:400px |1={{clade |label1=Hymenophylloideae |1=''Hymenophyllum'' |label2=Trichomanoideae |2={{clade |label1=Trichomaneae |1={{clade |1=''Callistopteris'' |2={{clade |1={{clade |1=''Cephalomanes'' |2=''Abrodictyum'' }} |2={{clade |1=''Abrodictyum obscurum'' |2=''Trichomanes'' s.s. }} }} }} |label2=Didymoglosseae |2={{clade |1=''Polyphlebium'' |2={{clade |1=''Didymoglossum'' |2={{clade |1=''Vandenboschia'' |2=''Crepidomanes'' }} }} }} }} }} }} }}
*'''Hymenophylloideae''' (the "hymenophylloid" clade): **{{txil|Hymenophyllum|Sm. 1793}} – about 250 species ***subg. {{tx|Hymenophyllum|}} – about 100 species ***subg. {{tx|Sphaerocionium|(C.Presl) C.Chr. 1934}} – about 70 species ***subg. {{tx|Mecodium|C.Presl ex Copel. 1937}} – more than 35 species ***subg. {{tx|Globosa|(Prantl) Ebihara & K.Iwats. 2006}} – about 25 species ***subg. {{tx|Pleuromanes|(C.Presl) Ebihara & K.Iwats. 2006}} – 5 species ***subg. {{tx|Myrmecostylum|(C.Presl) Ebihara & K. Iwats. 2006}} – at least 8 species ***subg. {{tx|Hymenoglossum|(C.Presl) R.M.Tryon & A.F.Tryon 1981}} – at least 3 species ***subg. {{tx|Fuciformia|Ebihara & K.Iwats. 2006}} – 2 species ***subg. {{tx|Diploöphyllum|(Bosch) Ebihara & K.Iwats. 2006}} – 1 species ***subg. {{tx|Cardiomanes|(C. Presl) Ebihara & K.Iwats. 2006}} – 1 species *'''Trichomanoideae''' (the "trichomanoid" clade) (sometimes all included in a single broad genus ''Trichomanes'' with about 400 species): **{{txil|Didymoglossum|Desv. 1827}} – more than 30 species ***subg. {{tx|Didymoglossum|}} – more than 20 species ***subg. {{tx|Microgonium|(C.Presl) Ebihara & K.Iwats. 2006}} – more than 10 species **{{txil|Crepidomanes|(C.Presl) C.Presl 1849}} – more than 30 species ***subg. {{tx|Crepidomanes|}} ***subg. {{tx|Nesopteris|(Copel.) Ebihara & K.Iwats. 2006}} **{{txil|Polyphlebium|Copel. 1938}} – about 15 species **{{txil|Vandenboschia|Copel. 1938}} – more than 15 species ***subg. {{tx|Vandenboschia|}} – more than 15 species ***subg. {{tx|Lacosteopsis|(Prantl) Ebihara & K.Iwats. 2006}} – at least 2 species **{{txil|Abrodictyum|C.Presl 1843}} – about 25 species ***subg. {{tx|Abrodictyum|}} – about 15 species ***subg. {{tx|Pachychaetum|(C.Presl) Ebihara & K.Iwats. 2006}} – more than 10 species **{{txil|Trichomanes|L. 1753}} – more than 60 species ***subg. {{tx|Afrotrichomanes|Dubuisson & Ebihara 2021}} ***subg. {{tx|Davalliopsis|(Bosch) Ebihara & K.Iwats. 2006}} – at least 1 species ***subg. {{tx|Feea|(Bory) Hook. 1844}} – more than 5 species ***subg. {{tx|Lacostea|(Bosch) C. Chr. 1906}} – more than 4 species ***subg. {{tx|Trichomanes|}} – more than 30 species **{{txil|Cephalomanes|C.Presl 1843}} – about 4 species **{{txil|Callistopteris|Copel. 1938}} – about 5 species
==Distribution and habitat== 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 (often occurring solely as gametophytes) to the humid eastern third of the continent and the rainforests of the Pacific Northwest.
==References== {{Reflist}}
{{Fern classification}} {{Taxonbar|from=Q1066700}} {{Authority control}}
Category:Fern families Category:Hymenophyllales