Osmundastrum

Last updated

Osmundastrum
Temporal range: NorianHolocene
Osmundastrum cinnamomeum May2015.jpg
Developing spore-bearing frond and several sterile fronds in late spring,
Osmundastrum-Pulchellum-rhizome.jpg
Fossil of a Osmundastrum Pulchellum rhizome
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Order: Osmundales
Family: Osmundaceae
Genus: Osmundastrum
C.Presl
Type species
Osmundastrum cinnamomeum
(L.) C.Presl
Species
Synonyms
  • Osmunda (Osmundastrum) Presl 1845

Osmundastrum is genus of leptosporangiate ferns in the family Osmundaceae with one living species, Osmundastrum cinnamomeum , the cinnamon fern. The modern species is native to the Americas and Asia, growing in swamps, bogs and moist woodlands. Fossil records of the genus extend into the Triassic.

Contents

Characteristics

Fossil and extant members of the genus Osmundastrum exhibit a high degree of anatomical and morphological consistency, suggesting long-term structural stability within the lineage. Anatomical features such as an ectophloic dictyoxylic siphonostele, homogeneous prosenchymatous pith, and horseshoe-shaped leaf traces are present in both fossil specimens, such as Osmundastrum gvozdevae from the Middle Jurassic of Russia, and the extant species Osmundastrum cinnamomeum. Osmundastrum pulchella from the Jurassic of Sweden had a rhizome structure similar to modern Osmundastrum, including a medullated stele with regularly spaced leaf gaps, sclerenchymatous petioles. Members of this genus are deciduous and herbaceous. The fertile spore-bearing fronds are erect. [4]

Classification

Spore-bearing frond Osmundastrum cinnamomeum bsl.JPG
Spore-bearing frond

Traditionally, the members of the genus Osmundastrum have been classified as Osmunda cinnamomea L. However, recent genetic and morphological evidence (Metzgar et al. 2008; Jud et al. 2008) clearly demonstrate that the cinnamon fern is a sister species to the entire rest of the living Osmundaceae. Cladistically, it is either necessary then to include all species of the Osmundaceae, including Todea and Leptopteris in the genus Osmunda , or else it is necessary to segregate the genus Osmundastrum. O. cinnamomeum is the sole living species in the genus, [5] although it is possible that some additional fossils should be assigned to Osmundastrum. [6]

Formerly, some authors included the interrupted fern, Osmunda claytoniana , in the genus or section Osmundastrum, because of its gross apparent morphological similarities. However genetic and morphological studies seem to show it is closer the genus Osmunda and this was shown when it was able to produce a hybrid species with the American Royal Fern while no known hybrids like this exist for Osmundastrum. However, detailed morphology and genetic analysis have proven that the interrupted fern is actually a true Osmunda. This is borne out by the fact that it is known to hybridize with the American royal fern, Osmunda spectabilis to produce Osmunda × ruggii in a family in which hybrids are rare, while Osmundastrum cinnamomeum has no known hybrids.

Osmundastrum cinnamomeum is considered a living fossil because it has been identified in the geologic record as far back as 75 million years ago. [6]


Fossil distribution

Fossil evidence assigned to the genus Osmundastrum indicates a broad prehistoric geographic range extending across multiple continents from the Triassic through the Cretaceous. Fossils identified as either definitive members of Osmundastrum or morphologically consistent with the genus have been recovered from North America, Oceania, Europe, Asia, and Antarctica, suggesting that the lineage was both widespread and ecologically versatile during the Mesozoic. The oldest member of the genus is O. indentatum from the Triassic of Tasmania, Australia. [7] In the Southern Hemisphere, Triassic permineralized rhizomes found in Antarctica and assigned to Ashicaulis woolfei display stem anatomy consistent with early Osmundastrum, including a dictyoxylic siphonostele and stipular frond bases. Although A. woolfei is not definitively placed within the crown group of Osmundastrum, it likely represents a stem lineage, indicating the presence of Osmundastrum-like ferns in high southern latitudes during the Triassic. Despite this extensive prehistoric range, today the genus is represented by a single extant species, Osmundastrum cinnamomeum, which is native to the Americas and parts of Asia. The reduction in species number and geographic contraction likely reflect a combination of environmental, ecological, and evolutionary pressures that took place from the Late Cretaceous through the Cenozoic. One contributing factor appears to be the climatic and ecological shifts that occurred during and after the Cretaceous–Paleogene (K–Pg) boundary. The global climatic cooling and drying trends of the Paleogene would have restricted the moist, temperate habitats favored by osmundaceous ferns. Fossils such as Osmundastrumprecinnamomeum from the Paleocene of North America demonstrate that members of the genus were still present shortly after the K–Pg extinction event, but show no evidence of further diversification. This suggests that while Osmundastrum survived the mass extinction, it did not undergo a significant post-Cretaceous radiation. [3] The species also underwent extreme evolutionary conservatism has likely contributed to its survival, but may also explain why the genus did not diversify further or adapt to new environments. The modern species has remained in a state of punctuated equilibrium since the Campanian stage of the Cretaceous. [3]

References

  1. Bazhenova, N. V.; Bazhenov, A. V. (2019). "Stems of a New Osmundaceous Fern from the Middle Jurassic of Kursk Region, European Russia" . Paleontological Journal. 53 (5): 540–550. Bibcode:2019PalJ...53..540B. doi:10.1134/S0031030119050034. S2CID   203848747 . Retrieved 9 November 2021.
  2. 1 2 Bomfleur, B.; Grimm, G. W.; McLoughlin, S. (2017). "The fossil Osmundales (royal ferns)—a phylogenetic network analysis, revised taxonomy, and evolutionary classification of anatomically preserved trunks and rhizomes". PeerJ. 5: e3433. doi: 10.7717/peerj.3433 . PMC   5508817 . PMID   28713650.{{cite journal}}: CS1 maint: article number as page number (link)
  3. 1 2 3 Benjamin Bomfleur; Guido W. Grimm; Stephen McLoughlin (2017). "The fossil Osmundales (Royal Ferns)—a phylogenetic network analysis, revised taxonomy, and evolutionary classification of anatomically preserved trunks and rhizomes". PeerJ. 5: e3433. doi: 10.7717/peerj.3433 . PMC   5508817 . PMID   28713650.{{cite journal}}: CS1 maint: article number as page number (link)
  4. Bazhenova, N. V.; Bazhenov, A. V. (September 2019). "Stems of a New Osmundaceous Fern from the Middle Jurassic of Kursk Region, European Russia" . Paleontological Journal. 53 (5): 540–550. doi:10.1134/s0031030119050034. ISSN   0031-0301.
  5. Alan S. Weakley (April 2008). "Flora of the Carolinas, Virginia, and Georgia, and Surrounding Areas".
  6. 1 2 Jud, Nathan, Gar W. Rothwell, and Ruth A. Stockey (2008). "Todea from the Lower Cretaceous of western North America: implications for the phylogeny, systematics, and evolution of modern Osmundaceae". American Journal of Botany. 95 (3): 330–339. doi: 10.3732/ajb.95.3.330 . PMID   21632358.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. Bomfleur, Benjamin; Grimm, Guido W.; McLoughlin, Stephen (2017-07-11). "The fossil Osmundales (Royal Ferns)—a phylogenetic network analysis, revised taxonomy, and evolutionary classification of anatomically preserved trunks and rhizomes". PeerJ. 5: e3433. doi: 10.7717/peerj.3433 . ISSN   2167-8359. PMC   5508817 . PMID   28713650. S2CID   12235529.{{cite journal}}: CS1 maint: article number as page number (link)

Further reading