Lepidodendron

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Lepidodendron
Temporal range: Early Carboniferous–Late Permian
Trunk fragment, showing leaf base scars
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Lycophytes
Class: Lycopodiopsida
Order: †Lepidodendrales
Family: †Lepidodendraceae
Genus: †Lepidodendron
Sternberg, 1820
Species
  • L. aculeatum Sternberg 1820
  • L. batovii Chachlov 1948
  • L. obovatum Sternberg 1820
  • L. whitehillianum Anderson & Anderson 1986
Synonyms
  • Dimicheleodendron B.A.Thomas & C.J.Cleal

Lepidodendron is an

club mosses", the genus was actually more closely related to modern quillworts than to modern club mosses. In the form classification system used in paleobotany
, Lepidodendron is both used for the whole plant as well as specifically the stems and leaves.

Etymology

The name Lepidodendron comes from the Greek λεπίς lepis, scale, and δένδρον dendron, tree.

Description and biology

Overview

Restoration
Lepidostrobus, the strobilus of Lepidodendron lycophytes

Lepidodendron species were comparable in size to modern trees. The plants had tapering trunks as wide as 2 m (6.6 ft) at their base that rose to about 40 m (130 ft)[2] and even 50 m (160 ft),[1] arising from an underground system of horizontally spreading branches that were covered with many rootlets. Though the height of the lycopsids make the plants similar to modern trees, the constant dichotomy of branches created a habit that contrasts with that of modern trees. At the ends of branches were oval-shaped strobili called Lepidostrobus that had a similar shape to modern cones of a spruce or fir.[3]

Stem

Leaf scars shown on a Lepidodendron. The "diamond shape" or scale impressions are common indicators of the leaf scars from Lepidodendron lycophytes.

The stem of the lycopsids had a

Picea species, as leaf scars formed peg-like projections that stretched and tore as the bark stretched. To resist the bending force of wind, Lepidodendron depended on their outer bark rather than their vascular tissues, as compared to modern trees that rely mostly on their central mass of wood.[3]

Leaves

Leaf of Lepidodendron

The leaves of the lycopsid were needle-like and were densely spiraled about young shoots, each possessing only a single

vein. The leaves were similar to those of a fir in some species and similar to those of Pinus roxburghii in others, though in general the leaves of Lepidodendron species are indistinguishable from those of Sigillaria species. The decurrent
leaves formed a cylindrical shell around branches. The leaves were only present on thin and young branches, indicating that, though the lycopsid were evergreen, they did not retain their needles for as long as modern conifers. The leaf-cushions were fusiform and elongated, growing at most to a length of 8 cm (3 in) and a width of 2 cm (3⁄4 in). The middle of leaf-cushions were smooth, where leaf scars were created when an abscission layer cut a leaf from its base. Each leaf scar was composed of a central circular or triangular scar and two lateral scars that were smaller and oval-shaped. This central scar marks where the main vascular bundle of the leaf connected to the vascular system of the stem. This xylem bundle was composed only of primary trachea.[citation needed] The two outer scars mark the forked branches of a strand of vascular tissue that passed from the cortex of the stem into the leaf. This forked strand is sometimes referred to as the "parichnos". Surrounding this strand were parenchyma cells and occasionally thick-walled elements. Surrounding both conducting tissues was a broad sheath of transfusion tracheids. Below the leaf scar the leaf-cushion tapered to a basal position. In this tapering area, circular impressions with fine pits were present. These impressions were continuous with the parichnos scars near the top of the tapering portion. This is because the impressions are formed by aerenchyma tissue that developed in closely with the parichnos. Above the leaf scar was a deep triangular impression known as the "ligular pit" for its similarities to the ligule of Isoetes. In some leaf-cushions a second depression was present above the ligular pit. Though its purpose is unclear, it has been suggested that the depression may mark the position of a sporangium. As the branch of a Lepidodendron lycopsid grew the leaf-cushion only grew to a certain extent, past which the leaf-cushion stretched. This stretching widened the groove that separated the leaf-cushions, creating a broad, flat channel.[3]

Underground Structures

The underground structures of Lepidodendron and similar lycopsid species known from the fossil record including

rhizomes similar to Isoetes. These rhizomorphic axes were shoot-like, and dichotomous branching of the rootlets structured the stigmarian systems. Rootlet scars can be seen from Stigmaria fossils where the root hairs used to be attached.[6] Hyphae are occasionally present in the tissues of Lepidodendron lycopsids, indicating the presence of mycorrhizal associations.[7]

Decay

Lepidodendron sp. bark from the Estonian Museum of Natural History.

Different fossil genera have been described to name the various levels of decay in Lepidodendron bark fossils. The name Bergeria describes stems that have lost their epidermises, Aspidiariu is used when cushions have been removed by deep decay, and Knorria is used when the leaf cushions and the majority of cortical tissues has decayed, with a shallow "fluted" surface remaining. However, it has been suggested that these are more likely growth forms than preserved bark types, as entire fossilized trunks have been discovered with dissimilar forms; if decay is assumed to be constant throughout the trunk, then different forms indicate growth rather than levels of decay. It is likely that the trunk of Lepidodendron lycopsids were subject to the growth forms Knorria, Aspidiaria, and Bergeria progressing up the trunk, respectively.[8]

Growth and reproduction

Reconstruction of a juvenile Lepidodendron, showing the unbranched trunk with leaves

During the early stages of growth, Lepidodendron grew as single, unbranched trunk, with leaves growing out of the scale leaf bases (cushions). Towards the end of the lycopod growth, the leaves on the lower part of the trunk were shed, and in Lepidodendron, the upper part of the trunk

sporangia situated on fertile stems that grew on or near the main trunk. The fertile stems grew together in cone-like structures that clustered at the tips of branches.[10]

Distribution

The lack of

latitudinal range of 120°.[4]

Extinction

In

Permian-Triassic extinction event.[11][13]

Gallery

  • Lepidodendron sp. bark from the Pottsville Group, Lower Pennsylvanian
    Lepidodendron sp. bark from the
    Pottsville Group
    , Lower Pennsylvanian
  • Lepidodendron elegans
    Lepidodendron elegans
  • Lepidodendron aculeatum
    Lepidodendron aculeatum
  • Lepidodendron lycopodioides
    Lepidodendron lycopodioides
  • Life restoration
    Life restoration
  • Restoration of Lepidodendron with leafy branches
    Restoration of Lepidodendron with leafy branches
  • Lepidodendron bark from Joggins, Nova Scotia, Canada
    Lepidodendron bark from Joggins, Nova Scotia, Canada
  • Lepidodendron fossil stumps from Fossil Grove, Glasgow, Scotland
    Lepidodendron fossil stumps from Fossil Grove, Glasgow, Scotland
  • Lepidodendron sp. stem impression displayed at a collection held in the National Museum of Brazil
    Lepidodendron sp. stem impression displayed at a collection held in the National Museum of Brazil
  • Various Lepidodendron diagrams from the Geological Survey of Pennsylvania
    Various Lepidodendron diagrams from the Geological Survey of Pennsylvania
  • External mold of Lepidodendron from the Upper Carboniferous of Ohio.
    External mold of Lepidodendron from the
    Upper Carboniferous of Ohio
    .
  • 1911 reconstruction of a mature Lepidodendron, showing dichotomous branching at the top of the trunk
    1911 reconstruction of a mature Lepidodendron, showing dichotomous branching at the top of the trunk

See also

References

  1. ^ a b V. V. Alekhin (1961). Geografiia rastenii s osnovani botaniki (Geography of plants and basics of botany). Gos. nauchno-pedagog. izd-vo. p. 167. Retrieved 2020-10-05.
  2. ^ A. V. Lopatin (2012). Палеонтологический музей имени Ю.А. Орлова (The Orlov Museum of Paleontology). Moscow: PIN RAN. p. 56.
    ISBN 978-5-903825-14-1
    . Retrieved 2020-10-05.
  3. ^ a b c Seward, Albert Charles (1898). Fossil plants: for students of botany and geology. Vol. 1. Cambridge University Press. pp. 93–192.
  4. ^ a b Vulf, Evgenii Vladimirovich and Brissenden, Elizabeth (1943). An introduction to historical plant geography. Chronica Botanica Company. pp. 176–177.{{cite book}}: CS1 maint: multiple names: authors list (link)
  5. ISBN 9780226580838
    .
  6. PMC 4914198
    .
  7. doi:10.1016/j.crpv.2007.09.006
    .
  8. doi:10.1002/gj.3350110102.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  9. ^
    PMID 29282734
    .
  10. ISBN 9780472082803
    .
  11. ^
    ISSN 2524-4507
    .
  12. ISSN 0305-8719
    .
  13. doi:10.1016/j.earscirev.2022.104136
    .

Further reading

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