# Taxonomy and systematics of Hymenophyllaceae
The **taxonomy and systematics of Hymenophyllaceae**, a family of ferns known as filmy ferns and bristle ferns, has been contested for over a century because the traditional division into two genera based on sorus shape does not match the family's evolutionary history.[1](https://sites.duke.edu/pryerlab/files/2017/12/pryer-et-al-ajb-2001.original.pdf) Molecular studies place the family as a basal lineage of the leptosporangiate ferns, with more than 600 species.[1](https://sites.duke.edu/pryerlab/files/2017/12/pryer-et-al-ajb-2001.original.pdf) The two clades are estimated to have diverged in the Middle Jurassic, about 172 Ma,[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf) and the oldest convincing fossil, *Hopetedia praetermissa* from the Upper Triassic of North Carolina, shows the family has existed since at least the Upper Triassic.[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf) In 2006, Atsushi Ebihara and Kunio Iwatsuki revised the taxonomy, placing all hymenophylloid species in a single genus *Hymenophyllum* and assigning the eight trichomanoid subclades to eight corresponding genera.[7](https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/439/946)
Its taxonomy has been contested for over a century, because the traditional division into two genera based on sorus (cluster of spore-producing structures on a fern frond) shape does not match the family's evolutionary history, which molecular phylogenetics has now mapped in detail.
| Key facts | |
|---|---|
| Family | Hymenophyllaceae (filmy ferns and bristle ferns) |
| Estimated divergence of the two clades | Middle Jurassic, about 172 Ma[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf) |
| Oldest convincing fossil | *Hopetedia praetermissa*, Upper Triassic of North Carolina[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf) |
## Higher-level classification
The linear sequence of Christenhusz et al.
## Generic delimitation disputes
Traditionally, only two genera were recognized: **Hymenophyllum**, with bivalved involucres, and **Trichomanes** sensu lato, with tubular involucres.[5](https://reflora.jbrj.gov.br/downloads/PTER2.pdf) The involucres are the protective structures around the sori, and they were long the principal character separating the two groups.[1](https://sites.duke.edu/pryerlab/files/2017/12/pryer-et-al-ajb-2001.original.pdf)
This bigeneric system was repeatedly challenged. Kunio Iwatsuki, a pteridologist who later co-authored the 2006 generic revision, noted in 1977 that involucral types form a continuous series from cup-shaped to bivalved, and he rejected the two-genus classification in favor of eight genera.[1](https://sites.duke.edu/pryerlab/files/2017/12/pryer-et-al-ajb-2001.original.pdf) Morton's 1968 scheme kept the two classical genera and added four monotypic genera, *Hymenoglossum*, *Serpyllopsis*, *Rosenstockia*, and *Cardiomanes*.[1](https://sites.duke.edu/pryerlab/files/2017/12/pryer-et-al-ajb-2001.original.pdf) None of these earlier classifications gained more than limited regional acceptance.[6](https://repository.naturalis.nl/pub/525675/BLUM2006051002002.pdf)
## Molecular phylogenetics and the 2006 revision
For example, the traditional *Trichomanes* subtaxa *Pleuromanes* and *Cardiomanes* belong to the "hymenophylloid" clade.[6](https://repository.naturalis.nl/pub/525675/BLUM2006051002002.pdf) Earlier phylogenetic work with the *rbcL* gene had already established [Hymenophyllaceae](https://www.edgepedia.org/hymenophyllaceae) as a basal lineage of leptosporangiate ferns and showed the two-clade structure that later studies used, with hymenophylloid taxa serving as out-groups in analyses of the trichomanoid ferns.[1](https://sites.duke.edu/pryerlab/files/2017/12/pryer-et-al-ajb-2001.original.pdf) • [3](https://comptes-rendus.academie-sciences.fr/biologies/articles/10.1016/j.crvi.2011.07.009/)
To reflect these findings, Atsushi Ebihara and Kunio Iwatsuki revised the taxonomy in 2006, placing all species of the "hymenophylloid" clade in a single genus *Hymenophyllum* and assigning the eight clear "trichomanoid" subclades to eight corresponding genera.[7](https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/439/946) A modern classification scheme on these lines underlies the family treatment in the [Flora of China](https://www.edgepedia.org/flora-of-china), co-authored by Ebihara and Iwatsuki.[4](https://www.iplant.cn/foc/pdf/Hymenophyllaceae.pdf)
**Classification since 2006** has not been stable. Smith et al. (2006) and Christenhusz et al.
## Divergence times and habit evolution
Using a two-gene dataset (*rbcL* plus *rps4*), Hennequin and colleagues estimated that the initial divergence within the family, giving rise to the trichomanoid and hymenophylloid clades, occurred in the Middle Jurassic, about 172 Ma.[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf) The hymenophylloid crown group began diversifying only in the [Cretaceous](https://www.edgepedia.org/cretaceous), a considerable delay relative to the trichomanoids.[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf) Ancestral habit reconstruction suggests the filmy ferns were ancestrally terrestrial, with epiphytism evolving several times independently during the Cretaceous.[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf)
## Fossil record
A fossil from the Upper Triassic of North Carolina, *Hopetedia praetermissa*, described by Axsmith et al. in 2001, is considered the oldest convincing representative of the Hymenophyllaceae, showing that the family has existed since at least the Upper Triassic.[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf) Several fossils from the [Paleozoic](https://www.edgepedia.org/paleozoic) or early Mesozoic have been assigned to the form genera *Hymenophyllites*, *Trichomanites*, or *Trichomanides*, but the affinity of these fossils to the Hymenophyllaceae is quite uncertain.[2](https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf)
## References
1. Pryer, K. M. et al. (2001). rbcl phylogeny of Hymenophyllaceae. American Journal of Botany. https://sites.duke.edu/pryerlab/files/2017/12/pryer-et-al-ajb-2001.original.pdf
2. Hennequin, S. et al. (2008). Divergence Times and the Evolution of Epiphytism in Filmy Ferns Revisited. International Journal of Plant Sciences. https://sites.duke.edu/pryerlab/files/2017/12/hennequin-et-al-ijps-2008.original.pdf
3. Anatomical diversity and regressive evolution in trichomanoid filmy ferns (Hymenophyllaceae): A phylogenetic approach. Comptes Rendus Biologies. https://comptes-rendus.academie-sciences.fr/biologies/articles/10.1016/j.crvi.2011.07.009/
4. Hymenophyllaceae. Flora of China. https://www.iplant.cn/foc/pdf/Hymenophyllaceae.pdf
5. [A TAXONOMIC REVISION OF HYMENOPHYLLACEAE, reflora.jbrj.gov.br](https://reflora.jbrj.gov.br/downloads/PTER2.pdf)
6. [A Taxonomic Revision of Hymenophyllaceae, Blumea / Naturalis Repository](https://repository.naturalis.nl/pub/525675/BLUM2006051002002.pdf)
7. [Disentangling the diversity and taxonomy of Hymenophyllaceae (Hymenophyllales, Polypodiidae) in the Comoros, europeanjournaloftaxonomy.eu](https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/439/946)
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*Topic: Encyclopedia › Life and health › Plants and algae › Ferns and lycophytes › Polypod fern families › Filmy ferns (Hymenophyllaceae) › Taxonomy and systematics*
*Initially written Sep 17, 2026 · Edited: Oct 15, 2026; Oct 25, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license