Osmundaceae

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Osmundaceae
Temporal range: Late Permian–Recent
Osmunda regalis
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Subclass: Polypodiidae
Order: Osmundales
Link
Family: Osmundaceae
Martinov
Type genus
Osmunda
Genera

Osmundaceae (royal fern family) is a family of

sporangia in Claytosmunda, Osmunda, Osmundastrum, and Plensium (subtribe Osmundinae[1]). In these genera the sporangia are borne naked on non-laminar pinnules, while Todea and Leptopteris (subtribe Todinae[1]
) bear sporangia naked on laminar pinnules. Ferns in this family are larger than most other ferns.

Description

The stems of Osmundaceae contain

siphonostele; that is, a ring of phloem occurs on the outside only of a ring of xylem, which surrounds pith (and no other vascular tissue).[2]
sclerenchymatous leaf bases and intermixed roots[4] can form a woody trunk when the stem emerges above ground, up to 1 meter (3.3 ft) in Todea barbara.[5] Extinct members of the family, which flourished during the Mesozoic, could reach the stature of trees and be termed tree ferns.[6] The leaves are either holodimorphic, with separate fertile and sterile fronds assuming an entirely different structure, or have fertile and sterile portions of the frond very distinct in structure.[2]

Sporangia in the Osmundaceae are large, and open at a slit on the top; the annulus that drives the sporangium opening is on the side. 128 to 512 spores are typically present. The spores are green, nearly round, and trilete.[2][7] The spores germinate into gametophytes, which are green (photosynthetic) and grow at the surface. They are large and heart-shaped. The base chromosome number for members of the order is 22.[2]

Taxonomy

Smith et al. (2006) carried out the first higher-level

phylogenic relationship is shown in the following cladogram, where Osmundales is seen as a sister to all other members of the subclass.[10]

Polypodiidae

Subdivision

In the Pteridophyte Phylogeny Group classification (2016) Osmundales consists of the single family Osmundaceae, six genera, and an estimated 18 species[9] (Christenhusz and Byng give 25 species).[11]

The three genera Osmunda, Leptopteris, and Todea were recognized as members of Osmundaceae by Smith et al. (2006)

monophyletic.[12]

The first molecular phylogeny

Osmunda claytoniana
.

The following phylogram shows the relationship between the Osmundaceae genera and subtaxa, according to Metzgar et al.:[12]

Osmundaceae

Osmundastrum (=Osmunda cinnamomea) 1 extant species

Todea 2 extant species

Leptopteris 6 extant species

Osmunda

subgenus Claytosmunda (=

Osmunda claytoniana
) 1 species

subgenus Plenasium 4 extant species

subgenus Osmunda 4 extant species

The circumscription of the order and its families was not changed, and its placement remained the same in subsequent classifications including Chase and Reveal (2009),

Chase (2014).[18] The find of an exceptionally well preserved Jurassic fossil[19] intermediate between genus Osmunda (as shown above) and Osmundastrum lead to a re-analysis of Metzgar et al.'s data, which revealed that the Osmundaceae root used above may be wrong[20] and a tree-branching
artefact (all other ferns are genetically very distant from the Osmundaceae), and allowing the following classification:

Osmundaceae
Osmunda

subgenus Osmundastrum

subgenus Claytosmunda

subgenus Plenasium

subgenus Osmunda

A molecular dating study using Metzgar et al.'s data and a comprehensive set of rhizome and leaf fossils estimated that (sub)generic differentiation within Osmundaceae started by the Triassic and was finished by the Early Cretaceous with the formation of Osmunda and Plenasium. Accordingly, the PPG I classification of 2016 continues to place Osmundales in Polypodiidae, but splits Osmunda further by elevating its subgenera to genera (Claytosmunda, Plenasium). The following cladogram reproduces the PPG I concept for the extant members of the family:[9]

Osmundaceae

Osmundastrum (Alternative A: outgroup-inferred root in multigene trees)

Osmundastrum (Alternative B[20][21])

Claytosmunda (=

Osmunda claytoniana
)

Plenasium 4 species

Osmunda 4 species

The new system was used in a comprehensive taxonomic evaluation of Osmundales rhizome fossils,[1] who provide a polytomous key using anatomical features of Osmundaceae rhizomes and an updated ‘evolutionary’ (non-cladistic) classification of fossil and extant Osmundales (see classification concepts for groups including extinct members), which can be tentatively transferred into the following cladogram (monophyla in bold, polytomies reflect unresolved relationships)

Osmundales

Bathypteris † monotypic, Late Permian

Guaireaceae †
Guaireoideae †

Guirea † mono- or paraphyletic with 2 species, Late Permian to Middle Triassic

Zhongmingella monotypic, late Permian Changhsingian

Lunea † monotypic, Early Jurassic

Itopsidemoideae †

Donwelliacaulis † monotypic, Middle Triassic

Itopsidema (incl. Tiania) † 1–2 species, ?Late Permian to Middle Triassic

Osmundaceae

Anomorrheanomen dubium, Late Permian

Thamnopteroideae †

Thamnopteris † mono- or paraphyletic with 9 species, Late Permian

Chasmatopteris † monotypic, Late Permian

Osmundoideae

Palaeosmunda † 2–3 species, Late Permian to ?Late Triassic

Millerocaulis p.p.a †

Millerocaulis p.p.a † In total 29 species, Triassic to mid-Cretaceous

Osmundeae (modern Osmundaceae)
Todeinae

Todea 3 species, Early Cretaceous to present

Leptopteris possibly 5 species, ?Early Cretaceous to present

Osmundinae

Osmundastrum 4 (or more) species, Triassic to present

Claytosmunda b

Claytosmunda (Osmunda) claytoniana and potential precursors[21]

Plenasium

Subgenus Aurealcaulis † likely paraphyletic with 6 species, Early Cretaceous to ?mid-Eocene

2 intermediate species from the Paleocene and Eocene

Subgenus Plenasium 5 species, Paleocene to present

Osmunda 7 species, Paleocene to present

Osmundacaulis † 18 species, Jurassic to Cretaceous

Shuishengella † monotypic, Late Permian

Notes:
aMillerocaulis is a likely paraphyletic genus that includes forms ancestral to the modern Osmundaceae (classified as Osmundeae) as well as their potential sister lineages.
bThe morphology of Claytosmunda is primitive within the Osmundinae, and total evidence indicates that Osmunda and Plenasium likely evolved from a Claytosmunda-type ancestor, rendering the latter genus paraphyletic when Osmundaceae fossil should be considered.[20][21][1] The genus comprises 12 fossil rhizome species in addition to the sole surviving species.

Evolution

Bomfleur et al. state

Claytosmunda. The better understood rhizome fossil record indicates that the group was most diverse in the Permian, and already much reduced in the Triassic regarding the number of substantially different forms (see Bomfleur et al.[1]
and literature cited therein).

The first fossil representatives of the modern Osmundaceae (= tribus Osmundeae) include rhizome fossils with

Early Cretaceous, co-eval with the divergence between the sister genera Todea and Leptopteris.[21] The Osmundastrum-lineage diverged much earlier (probably Middle Triassic), which fits with the new classification of re-evaluated rhizome fossils originally included in Millercaulis. A comprehensive list of rhizome and leaf fossils associated with modern Osmundaceae (Osmundeae in the classification of Bomfleur et al.[1]) can be found at datadryad.org
.

The only explicit reconstruction regarding the evolution of morphological traits in Osmundaceae can be found in Miller's groundbreaking work.

rhizomatous with small, low-dissected steles.[25]

References

  1. ^ a b c d e f g h i Bomfleur et al. 2017.
  2. ^ a b c d e Smith et al. 2006, p. 710.
  3. ^ Moran 2004, p. 77.
  4. ^ Faull 1901, p. 384.
  5. ^ Hoshizaki & Moran 2001, pp. 526–527.
  6. ^ Moran 2004, pp. 144–145.
  7. ^ Moran 2004, pp. 77–78.
  8. ^ a b Smith et al. 2006.
  9. ^ a b c Pteridophyte Phylogeny Group 2016.
  10. ^ Lehtonen 2011.
  11. ^ Christenhusz & Byng 2016.
  12. ^ a b Metzgar et al. 2008.
  13. ^ Yatabe et al. 1999.
  14. ^ Smith et al. 2008.
  15. ^ Yatabe, Y.; et al. (2005). "Claytosmunda; a new subgenus of Osmunda (Osmundaceae)". Acta Phytotaxon. Geobot. 56: 127–128.
  16. ^ Chase & Reveal 2009.
  17. ^ Christenhusz et al. 2011.
  18. ^ Christenhusz & Chase 2014.
  19. S2CID 38248823
    .
  20. ^ a b c d Bomfleur et al. 2015.
  21. ^ a b c d Grimm et al. 2015.
  22. ^ Bomfleur et al. 2017, p. 2.
  23. S2CID 85319731
    .
  24. ^ a b Miller 1971.
  25. doi:10.7717/peerj.3433/supp-6. {{cite journal}}: Cite journal requires |journal= (help
    )

Bibliography

External links