Williamsonia (plant)

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Williamsonia
Temporal range: Middle Triassic–Late Cretaceous
Williamsonia harrisiana seed cone cross section.svg
Cross section of Williamsonia harrisiana (India, Jurassic - Early Cretaceous)
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Gymnosperms
Order:† Bennettitales
Family:† Williamsoniaceae
Genus:† Williamsonia
Carruth., 1870 [1]
Type species
Williamsonia gigas
Carruth., 1870 [1]

Williamsonia is a genus of plant belonging to Bennettitales, an extinct order of seed plants. Within the form classification system used in paleobotany, Williamsonia is used to refer to female seed cones, which are associated with plants that also bore the male flower-like reproductive structure Weltrichia. [2]

Contents

Description

The monosporiangiate [2] female Williamsonia seed cone (sometimes described as a "flower" though this does not imply homology with angiosperm flowers [3] ) consists of an ovulate receptacle enclosed by bracts (modified leaves), with the receptacle bearing sporophylls with terminal seeds/ovules, which are surrounded by interseminal scales. [4] The micropyle of the ovules varied from protruding above the cone to slightly sunken in, depending on the species. [2] The cones were of variable shape, with reported morphologies including pyriform (pear shaped), ovoid, subspheroidal, and oblate spheroid [2] and could be up to 15 centimetres (5.9 in) in diameter. As many as 25–50 ovules could be present in each cone. [5] The cone was borne on a peduncle, and grew at the apex of a branch. [6] [2] In at least some species, only one Williamsonia cone grew per active branch at any one time/season, while the cones from the preceding season/time developed into mature seed cones. [6] The cones have been suggested to be wind pollinated. [7] In at least some species, the cones increased in size during maturation, which might reflect the transformation of the interseminal scales into a fleshy coating possibly used to attract seed dispersers. [6]

Associated plant parts

Weltrichia sol, the male reproductive organ counterpart to the type species of Williamsonia, W. gigas scale bar = 20mm/~0.8 in Weltrichia sol.png
Weltrichia sol, the male reproductive organ counterpart to the type species of Williamsonia, W. gigas scale bar = 20mm/~0.8 in

Williamsonia is typically associated with the male flower-like reproductive structure Weltrichia. It is unclear whether the parent plants were monoecious (having both structures on one plant) or dioecious (where each plant only has one gender of reproductive organ). In Kimuriella densifolia from the Late Jurassic of Japan and Williamsonia gigas from the Middle Jurassic of England, the Williamsonia cone is associates with leaves assignable to the genus Zamites, [6] while Williamsonia carolinensis from the Late Triassic of North America is associated with leaves assigned to Eoginkgoites . [8] Kimuriella is thought to have been a divaricately branching, low growing shrub with a maximum height of 2–3 metres, with a growth form similar to that of Wielandiella , while Williamsonia gigas may have been more cycad-like. In Kimuriella and W. gigas, the axes (assigned to Bucklandia in W. gigas), which were up to 16 millimetres (0.63 in) and 40–50 millimetres (1.6–2.0 in) wide respectively, were densely covered with persistent leaf bases, which were apparently sloughed off in older branches. [6] The affinity of the cycad-like Williamsonia sewardiana from Early Cretaceous Rajmahal Hills of India [9] to the family Williamsoniaceae has been questioned, with some scholars suggesting that the species may represent an early species of Cycadeoidaceae instead. [10]

Taxonomy

Williamsonia sewardiana life restoration by MUSE - Science Museum, whose affinity to Williamsoniaceae has been questioned Williamsonia life restoration - MUSE.jpg
Williamsonia sewardiana life restoration by MUSE - Science Museum, whose affinity to Williamsoniaceae has been questioned

Williamsonia was originally described as Zamia gigas by William Crawford Williamson. [11] William Carruthers proposed the name Williamsonia in 1870, with the type species being W. gigas from the Middle Jurassic of England. [1] When originally specifying the genus, Carruthers specifically referred to the foliage, which modern authors usually assign to the foliage genus Zamites. However, later authors beginning with Tom Harris's 1969 publication The Yorkshire Jurassic Flora used Williamsonia to refer to the ovulate reproductive organs. [3]

Distribution

Fossils of Williamsonia are known spanning from the Middle Triassic [3] to Late Cretaceous, [7] and have been found worldwide, including in Europe, [12] Australia, [3] North America, [8] [7] East Asia [6] India [13] and South America. [14]

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Bennettitales is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales were amongst the most common seed plants of the Mesozoic, and had morphologies including shrub and cycad-like forms. The foliage of bennettitaleans is superficially nearly indistinguishable from that of cycads, but they are distinguished from cycads by their more complex flower-like reproductive organs, at least some of which were likely pollinated by insects.

<i>Cycadeoidea</i> Extinct genus of plants

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<i>Zamites</i> Extinct genus of bennettitalean foliage

Zamites is a genus of sterile foliage known from the Mesozoic of North America, Europe, India and Antarctica through the Eocene of North America. It was erected as a form taxon for leaves that superficially resembled the extant cycad Zamia, however it is now believed to belong to a similar but phylogenetically different group, the cyacadeoids (Bennettitales). The fronds are linear or lanceolate in shape, and pinnately compound, with pinnae with parallel veins and smooth margins, and symmetrical and constricted at the base where they are attached obliquely to the upper surface of the rachis. It has been interpreted as a Bennettitalean plant in the family Williamsoniaceae. It is associated with the ovulate cone Williamsonia and male cone Weltricihia.

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Nilssoniopteris is an extinct form genus of leaves belonging to the Bennettitales. Leaves are slender and often entire-margined (smooth-edged), though some species have dissected leaves with numerous small segments extending down to the rachis of the leaf. Nilssoniopteris-like leaves are distinguished by their syndetocheilic stomata, indicating bennettitalean affinities. Similar "taeniopterid" leaves are placed in the genus Nilssonia if their stomata are instead haplocheilic, or Taeniopteris if the cuticle is not preserved. Leaves of Nilssoniopteris vittata from the Middle Jurassic of England are associated with bisexual Williamsoniella reproductive structures.

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Eoginkgoites is an extinct form genus of bennettitalean leaves from the Late Triassic of North America. Despite its palmate (hand-shaped) appearance similar to some early ginkgo species, it belongs to a different gymnosperm order, the Bennettitales. The leaf is deeply segmented into five to seven narrow, club-shaped lobes which twist around a very short rhachis. This leads to an overall fan-shaped leaf situated at the end of a long petiole. The leaf has paracytic stomata and veins which strongly branch and lead to a marginal vein at the edge of each leaflet. These structural traits are all shared with benettitaleans. Williamsonia carolinensis, an ovule-bearing bennettitalean cone, has been found closely associated with Eoginkgoites leaves, seemingly confirming its benettitalean identity.

This paleobotany list records new fossil plant taxa that were to be described during the year 2023, as well as notes other significant paleobotany discoveries and events which occurred during 2023.

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Pararaucaria is a genus of conifer cone belonging to the extinct family Cheirolepidiaceae. Fossils are known from the Lower Jurassic to Early Cretaceous of North America, Europe, South America and Asia. It is associated with Brachyphyllum-type foliage.

<i>Weltrichia</i> Extinct genus of bennettitalean plant

Weltrichia is a genus belonging to the extinct seed plant group Bennettitales. It is a form genus representing flower-like male pollen-producing organs. It is associated with the female ovulate cone Williamsonia.

<i>Wielandiella</i> Extinct genus of bennettitalean plant

Wielandiella is an extinct genus of bennettitalean shrub known from the Late Triassic (Rhaetian) of Europe and Greenland, and the Middle Jurassic of China.

References

  1. 1 2 3 Seward, A. C. (2011). Fossil Plants: A Text-Book for Students of Botany and Geology. Cambridge, New York: Cambridge University Press. p. 421. ISBN   978-1-108-01597-4 . Retrieved February 7, 2012.
  2. 1 2 3 4 5 Stockey, Ruth A.; Rothwell, Gar W. (March 2003). "Anatomically Preserved Williamsonia (Williamsoniaceae): Evidence for Bennettitalean Reproduction in the Late Cretaceous of Western North America". International Journal of Plant Sciences. 164 (2): 251–262. doi:10.1086/346166. ISSN   1058-5893. S2CID   84997693.
  3. 1 2 3 4 McLoughlin, Stephen; Pott, Christian; Sobbe, Ian H. (March 2018). "The diversity of Australian Mesozoic bennettitopsid reproductive organs". Palaeobiodiversity and Palaeoenvironments. 98 (1): 71–95. doi: 10.1007/s12549-017-0286-z . ISSN   1867-1594.
  4. ↑ Rothwell, Gar W.; Crepet, William L.; Stockey, Ruth A. (2009). "Is the anthophyte hypothesis alive and well? New evidence from the reproductive structures of Bennettitales". American Journal of Botany. 96 (1): 296–322. doi: 10.3732/ajb.0800209 . PMID   21628190.
  5. ↑ Taylor, Thomas N.; Taylor, Edith L.; Krings, Michael (2009). "Cycadophytes". Paleobotany: The Biology and Evolution of Fossil Plants (2nd ed.). Amsterdam: Academic Press. p. 734. ISBN   978-0-12-373972-8 . Retrieved February 8, 2012.
  6. 1 2 3 4 5 6 Pott, Christian; Takimoto, Hideo (2022-04-01). "Kimuriella gen. nov. (Bennettitales), a Whole-Plant Bennettite from the Oxfordian (Upper Jurassic) Tochikubo Formation of Shidazawa, Minamisōma, Fukushima Prefecture, Northeast Japan". Paleontological Research. 26 (2). doi:10.2517/PR200020. ISSN   1342-8144. S2CID   247960229.
  7. 1 2 3 Stockey, Ruth A.; Rothwell, Gar W. (March 2003). "Anatomically Preserved Williamsonia (Williamsoniaceae): Evidence for Bennettitalean Reproduction in the Late Cretaceous of Western North America". International Journal of Plant Sciences . 164 (2): 251–262. doi:10.1086/346166. JSTOR   10.1086/346166. S2CID   84997693.
  8. 1 2 Pott, Christian; Axsmith, Brian J. (2015). "Williamsonia carolinensis sp. nov. and Associated Eoginkgoites Foliage from the Upper Triassic Pekin Formation, North Carolina: Implications for Early Evolution in the Williamsoniaceae (Bennettitales)". International Journal of Plant Sciences. 176 (2): 174–185. doi:10.1086/679471. ISSN   1058-5893. S2CID   44559347.
  9. ↑ Sahni B (1932) A petrified Williamsonia (W. sewardiana, sp. nov.) from the Rajmahal Hills, India. Palaeontol Ind 20:1–19
  10. ↑ Pott, Christian; McLoughlin, Stephen (June 2014). "Divaricate growth habit in Williamsoniaceae (Bennettitales): unravelling the ecology of a key Mesozoic plant group". Palaeobiodiversity and Palaeoenvironments. 94 (2): 307–325. doi:10.1007/s12549-014-0157-9. ISSN   1867-1594. S2CID   84440045.
  11. ↑ Reddy, S. M.; Chary, S. J. (2003). University Botany 2: Gymnosperms, Plant Anatomy, Genetics, Ecology. Vol. 2. New Delhi: New Age International. p. 12. ISBN   978-81-224-1477-6 . Retrieved February 8, 2012.
  12. ↑ ARBER, E. A. NEWELL (April 1919). "Remarks on the Organization of the Cones of Williamsonia gigas (L. & H.)". Annals of Botany. os-33 (2): 173–179. doi:10.1093/oxfordjournals.aob.a089706. ISSN   1095-8290.
  13. ↑ Bose, M. N. (July 1968). "A new species of Williamsonia from the Rajmahal Hills, India". Journal of the Linnean Society of London, Botany. 61 (384): 121–127. doi:10.1111/j.1095-8339.1968.tb00109.x.
  14. ↑ Barboni, Ronaldo; Dutra, Tânia Lindner (2013-02-01). "New "Flower" and Leaves of Bennettitales from Southern Brazil and their Implication in the Age of the Lower Mesozoic Deposits". Ameghiniana. 50 (1): 14. doi:10.5710/AMGH.28.11.2012.444. ISSN   0002-7014. S2CID   73521657.
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