Bennettitales

Source: Wikipedia, the free encyclopedia.

Bennettitales
Temporal range: Permian - Late Cretaceous,
Kungurian –Maastrichtian Possible Oligocene record
Restoration of a member of Williamsoniaceae by Thérèse Ekblom
Life restoration of "Williamsonia" sewardiana from the Early Cretaceous of India, which may represent an early member of Cycadeoidaceae
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Spermatophytes
Order: †Bennettitales
Engler, 1892
Families

Bennettitales (also known as cycadeoids) is an extinct

pollinated by insects.[1]

Although certainly gymnosperms sensu lato (cone-bearing seed plants), the relationships of bennettitaleans to other seed plants is debated. Their general resemblance to cycads is contradicted by numerous more subtle features of their reproductive systems and leaf structure. Some authors have linked bennettitaleans to angiosperms (flowering plants) and gnetophytes (a rare and unusual group of modern gymnosperms), forming a broader group known as Anthophyta. Molecular data contradicts this, with gnetophytes found to be much more genetically similar to conifers. The exact position of Bennettitales remains uncertain.

Description

Bennettitales foliage assigned to the genus Pterophyllum
Restoration of the willamsoniacean shrub Wielandiella angustifolia showing divaricate branching habit

Bennettitales are divided into two families, Cycadeoidaceae and Williamsoniaceae, which have distinct growth habits. Cycadeoidaceae had stout, cycad-like trunks with bisporangiate (containing both megaspores and microspores) strobili (cones) serving as their reproductive structures. Williamsoniaceae either had bisporangiate or monosporangiate cones, and distinctly slender and branching woody trunks.[1] The Williamsoniaceae grew as woody shrubs with a divaricate branching habit, similar to that of Banksia.[2] It has been suggested that Williamsoniaceae are a paraphyletic (not containing all descendants of a common ancestor) assemblage of all Bennettitales that do not belong to the Cycadeoidaceae.[2]

Foliage

In general, bennettitalean leaves are attached to the stem with a helical (corkscrew) arrangement. Some leaves (most species of

palmate appearance similar to early species of Ginkgo.[4]

The foliage of bennettitaleans resembles that of cycads to such an extent that the foliage of the two groups cannot be reliably distinguished based on gross morphology alone. However, fossil foliage which preserves the cuticle can be assigned to either group with confidence. The stomata of bennettitaleans are described as syndetocheilic. This means that the main paired guard cells develop from the same mother cells as the subsidiary cells which surround them. This contrasts with the haplocheilic stomata of cycads and conifers. In haplocheilic stomata, the ring of subsidiary cells are not derived from the same original structures as the guard cells. This fundamental difference is the main way to differentiate bennettitalean and cycad foliage.[5]

Cones and seeds

Diagram of male Williamsoniaceae reproductive structure Weltrichia. Labels: CFR Centrifugal ray; CPR Centripetal ray; MR Median ridge; FS Fibrous strand; PS Pollen sac position (in this case, pollen sac attachment); CC Central cup; RBA Resin (resinous) body or attractant; ST Stalk
Cross section of the female williamsoniaceous seed cone Williamsonia harrisiana

Like other gymnosperms, bennettitalean reproductive inflorescences come in the form of

microsporophylls. This contrasts with cycads, all of which lack discrete synangia and bear pollen on the abaxial (outer) surface of their microsporophylls.[6]

Many bennettitaleans are bisporangiate, where the pollen and ovules are hosted on the same (bisexual or hermaphrodite) cone. Cavities filled with curved synangia-bearing microsporophylls are encased by thin radiating structures, including thick, infertile interseminal scales and fertile sporophylls with ovules at their tips. The presence of ovules at the tips of sporophylls, rather than the tips of stems, is a major difference between the cones of bennettitaleans and gnetophytes. As the cone is fertilized and matures, the microsporophylls wither away and the ovules transform into seeds.[6]

Most bennettitaleans in the family Williamsoniaceae are instead monosporangiate, with separate pollen and ovule-producing (unisexual) cones on the same plant. The ovule-producing (female) cones (Williamsonia, etc.) are similar to mature bisporangiate cones, with interseminal scales and ovule-tipped sporophylls enclosed by bracts. Pollen-producing (male) cones (Weltrichia, etc.), on the other hand, feature an exposed crown of tapering microsporophylls with adaxial rows of synangia. The microsporophylls may host a single linear row of paired synangia, or instead synangia arranged in a pinnate (feather-shaped) pattern.[6]

micropyle. A long, narrow micropyle extending out of the seed is superficially similar to the condition in living gnetophytes. Once the seed is fertilized, the micropyle is sealed by a plug-shaped extension of the nucellus. Unlike living gymnosperms, the tip of the nucellus lacks a pollen chamber (receptacle for stored pollen). The integument is dense and thick, with many layers of differentiated cells. This contrasts with the thin, biseriate (two cell-layer) integument of gnetophytes. Bennettitaleans also lack another gnetophyte-like trait: a sheath of fused bracteoles enveloping the seed. Most integument cells are not unusual in size or shape. However, near the micropyle the innermost layer of integument cells become radially-oriented and elongated, partially closing in on the micropyle. The nucellus and integument are unfused above the chalaza (base of the seed), unlike cycads or gnetophytes, where the layers are fused for much of their height.[6]

Cycadeoidaceans have been suggested to have been self-pollinating, with their stems and cones buried underground,

wind-pollinated, with some species possibly pollinated by beetles.[9]

Several groups of Jurassic and Early Cretaceous insects possessed a long proboscis, and it has been suggested that they fed on nectar produced by bennettitalean reproductive structures, such as the bisexual williamsoniacean reproductive structure Williamsoniella, which had a long, narrow central receptacle which was likely otherwise inaccessible.[10] Early Cretaceous bennettitalean pollen has been found directly associated with a proboscis bearing fly belonging to the extinct family Zhangsolvidae, providing evidence that this family acted as pollinators for the group.[11] The interseminal scales of Bennettitales ovulate cones may have become fleshy at maturity, which could have potentially made then attractive to wild animals that served as seed dispersers.[12]

Taxonomy

History of discovery

The Cycadeoideaceae (originally “Cycadeoideae”) were named by English geologist

Bennettites named by Caruthers in the same publication, the name being in honour of British botanist John Joseph Bennett.[14][17] The order Bennettitales was erected by German botanist Adolf Engler in 1892, who recognised the group as separate from the Cycadales.[18]

Relationships to other seed plants

The

Gnetales and Erdtmanithecales, dubbed the "BEG group".[23] However, this proposal has been contested by other authors, who contend that these similarities are only superficial and do not indicate a close relationship.[24] A 2017 phylogeny based on molecular signatures of fossilised cuticles found that Bennettitales were more closely related to the Ginkgo+Cycads clade than conifers, and were closely related to Nilssonia and Ptilozamites.[25]

Evolutionary history

The oldest confirmed fossils of bennettitaleans are leaves of Nilssoniopteris shanxiensis, a species from the upper part of the Upper Shihhotse Formation in Shanxi Province, China.[5] This strata is dated to the early Kungurian stage of the early Permian (Cisuralian), around 281 million years ago.[26] Supposed Carboniferous-Permian records of Pterophyllum do not have conclusive bennettitalean affinities or have been reinterpreted as cycad foliage in the form genus Pseudoctenis.[27] True Permian records of benettitalean leaves are rare; outside of the Shihhotse Formation they are only found in the Late Permian (likely Changhsingian)-age Umm Irna Formation in Jordan.[5] This formation is notable for the early occurrence of other Mesozoic-style flora, including the earliest records of corystospermalean foliage (Dicroidium).[28] The order Fredlindiales (containing the genus Fredlindia) from the Late Triassic of Gondwana appears to be closely related to Bennettitales, but differs from it in some aspects of its reproductive organs.[16]

The bennettitalean fossil record reappeared in the Middle Triassic, and williamsoniaceans became globally distributed by the end of the period.[29][5] The oldest bennettitalean reproductive structures are small Williamsonia "flowers" from the Middle Triassic Esk Formation of Australia.[16] While Williamsoniaceae had a global distribution, Cycadeoidaceae appear to have been primarily confined to the western parts of Laurasia, and are primarily known from the Cretaceous.[16] Bennettitales were widespread and abundant during the Jurassic and Early Cretaceous, however Bennettitales severely declined during the Late Cretaceous, coincident with the rise of flowering plants, being mostly extinct by the end of the period, with the final known remains from the Northern Hemisphere being found in the polar latitude Kakanaut Formation in Chukotka, Russia, dating to the Maastrichtian, assignable to Pterophyllum.[30] A possible late record has been reported from the early Oligocene of eastern Australia and Tasmania, assignable to the genus Ptilophyllum, but no cuticle was preserved, making the referral inconclusive.[31]

Subgroups

Bennettitales is typically considered the sole order in the class Bennettitopsida Engler (1897) or Cycadeoideopsida Scott (1923). Most paleobotanists prefer the two families as used here, though some authors, such as Anderson & Anderson (2007), classify the order via a larger number of families.[33] Anderson & Anderson also classified the orders Fredlindiales Anderson & Anderson (2003)[34] and Pentoxylales Pilger & Melchior (1954) within Bennettitopsida.[33]

Gallery

References

  1. ^
    S2CID 13022302
    .
  2. ^
    S2CID 84440045
    .
  3. S2CID 232349931
    .
  4. S2CID 44559347
    .
  5. ^
    doi:10.3389/feart.2021.652699
    .
  6. ^
    PMID 21628190
    .
  7. ISBN 978-0-253-00199-3
    .
  8. ^ Frame, Dawn; Gottsberger, Gerhard (21 April 2023). "Diverse sexual strategies in fossil gymnosperms: pollination in the Bennettitales revisited". Phyton. 62/63.
  9. S2CID 85458053
    .
  10. S2CID 134847380
    .
  11. PMID 26166781
    .
  12. ISBN 978-0-521-59283-3
    , retrieved 2023-03-20
  13. doi:10.12705/652.16
    .
  14. ^
    doi:10.1111/j.1096-3642.1870.tb00201.x
    .
  15. doi:10.1111/j.1096-3642.1870.tb00200.x
    .
  16. ^
    S2CID 135237376
    .
  17. doi:10.5962/bhl.title.56947
    .
  18. ^ Engler, H.G.A. 1892. Syllabus der Vorlesungen über specielle und medicinisch-pharmaceutische Botanik. xxiii + 184 pp. Gebr. Borntraeger, Berlin
  19. doi:10.1111/j.1095-8339.1907.tb01074.x
    .
  20. S2CID 85709030
    .
  21. S2CID 83801635
    .
  22. PMID 29925623
    .
  23. S2CID 1198220
    .
  24. S2CID 84063572
    .
  25. S2CID 3604369
    .
  26. S2CID 234064909
    .
  27. S2CID 52253114
    .
  28. PMID 30573628
    .
  29. ^ Kustatscher, Evelyn; van Konijnenburg-van Cittert, Johanna H.A. (2005). "The Ladinian Flora (Middle Triassic) of the Dolomites: palaeoenvironmental reconstructions and palaeoclimatic considerations" (PDF). Geo.Alp. 2: 31–51.
  30. doi:10.1016/j.cretres.2017.09.013
    .
  31. S2CID 52885618
    .
  32. doi:10.1016/j.revpalbo.2023.104934
    .
  33. ^ a b Anderson, John M.; Anderson, Heidi M.; Cleal, Chris J. (2007). "Brief history of the gymnosperms: classification, biodiversity, phytogeography and ecology" (PDF). Strelitzia. 20: 1–280.
  34. ^ Anderson, John M.; Anderson, Heidi M. (2003). "Heyday of the gymnosperms: systematics and biodiversity of the Late Triassic Molteno fructifications". Strelitzia. 15: 1–308.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Bennettitales&oldid=1206678621"