page_title: Lycopodiopsida
section_title: Evolution
hierarchical_section_title: Lycopodiopsida / Evolution
caption_attribution_description: English: Lepidodendron external mold from the Upper Carboniferous of Ohio.
context_page_description: Lycopodiopsida is a class of herbaceous vascular plants known as lycopods, lycophytes or other terms including the component lyco-. Members of the class are called clubmosses, firmosses and quillworts. They have dichotomously branching stems bearing simple leaves called microphylls and reproduce by means of spores borne in sporangia on the sides of the stems at the bases of the leaves. Although living species are small, during the Carboniferous, extinct tree-like forms formed huge forests that dominated the landscape and contributed to coal deposits.
  The nomenclature and classification of plants with microphylls varies substantially among authors. A consensus classification for extant species was produced in 2016 by the Pteridophyte Phylogeny Group, which places them all in the class Lycopodiopsida, which includes the classes Isoetopsida and Selaginellopsida used in other systems. Alternative classification systems have used ranks from division to subclass. In the PPG I system, the class is divided into three orders, Lycopodiales, Isoetales and Selaginellales.
context_section_description: The Lycopodiopsida are distinguished from other vascular plants by the possession of microphylls and by their sporangia, which are lateral as opposed to terminal and which open (dehisce) transversely rather than longitudinally. In some groups, the sporangia are borne on sporophylls that are clustered into strobili. Phylogenetic analysis shows the group branching off at the base of the evolution of vascular plants and they have a long evolutionary history. Fossils are abundant worldwide, especially in coal deposits. Fossils that can be ascribed to the Lycopodiopsida first appear in the Silurian period, along with a number of other vascular plants. The Silurian Baragwanathia longifolia is one of the earliest identifiable species. Lycopodolica is another Silurian genus which appears to be an early member of this group. The group evolved roots independently from the rest of the vascular plants.
  From the Devonian onwards, some species grew large and tree-like. Devonian fossil trees from Svalbard, growing in equatorial regions, raise the possibility that they drew down enough carbon dioxide to change the earth's climate significantly. During the Carboniferous, tree-like forms (such as Lepidodendron and other "scale-trees" of the order Lepidodendrales) formed huge forests that dominated the landscape. Unlike modern trees, leaves grew out of the entire surface of the trunk and branches, but fell off as the plant grew, leaving only a small cluster of leaves at the top. The trees are marked with diamond-shaped scars where they once had leaves. Quillworts (order Isoetales) are considered their closest extant relatives and share some unusual features with these fossil trees, including the development of both bark, cambium and wood, a modified shoot system acting as roots, bipolar and secondary growth, and an upright stance. The remains of scale-trees formed many fossil coal deposits. In Fossil Park, Glasgow, Scotland, fossilized lycophyte trees can be found in sandstone.
  The Lycopodiopsida had their maximum diversity in the Pennsylvanian (Upper Carboniferous), particularly tree-like Lepidodendron and Sigillaria that dominated tropical wetlands. The complex ecology of these tropical rainforests collapsed during the Middle Pennsylvanian due to a change in climate. In Euramerica, tree-like species apparently became extinct in the Late Pennsylvanian, as a result of a transition to a much drier climate, giving way to conifers, ferns and horsetails. In Cathaysia (now South China), tree-like species survived into the Permian. Nevertheless, lycopodiopsids are rare in the Lopingian (latest Permian), but regained dominance in the Induan (earliest Triassic), particularly Pleuromeia. After the worldwide Permian–Triassic extinction event, members of this group pioneered the repopulation of habitats as opportunistic plants. The heterogeneity of the terrestrial plant communities increased markedly during the Middle Triassic when plant groups like horsetails, ferns, pteridosperms, cycads, ginkgos and conifers resurfaced and diversified quickly.
caption: External impression of Lepidodendron from the Upper Carboniferous of Ohio
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