Trimerophytopsida (or Trimeropsida) is a class of early vascular plants from the Devonian, informally called trimerophytes. It contains genera such as Psilophyton. This group is probably paraphyletic, and is believed to be the ancestral group from which both the ferns and seed plants evolved. Different authors have treated the group at different taxonomic ranks using the names Trimerophyta, Trimerophytophyta, Trimerophytina, Trimerophytophytina and Trimerophytales.

Temporal range: Devonian
Psilophyton dawsonii-rev
Fossil of Psilophyton dawsonii
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Class: Trimerophytopsida
A.S.Foster & E.M.Gifford 1974


  • Trimerophyta (orth. var.)
  • Psilophyta (orth. var.)
  • Trimerophytophyta Bold 1973
  • Trimerophytophytina Banks 1975
  • Psilophytophyta Zimmermann 1930
  • Psilophytophytina Kryshtofovich 1945


At first most of the early land plants other than the bryophytes (i.e. the polysporangiophytes) were placed in a single class Psilophyta, established in 1917 by Kidston and Lang.[1] As additional fossils were discovered and described, it became apparent that the Psilophyta were not a homogeneous group of plants. In 1968 Banks first proposed splitting this taxon into three groups, which he put at the rank of subdivision; he clarified his proposal in 1975. One of the three groups was the Trimerophytina.[2][3] The subdivision is based on the type genus Trimerophyton, which might be expected to produce 'Trimerophytophytina' as the name of the subdivision, but the International Code of Nomenclature for algae, fungi, and plants allows the 'phyton' part of a genus name optionally to be omitted before '-ophyta', '-ophytina' and '-opsida'.[4]

The group has also since been treated as a division under the name Trimerophyta[5] or Trimerophytophyta, as a class under the name Trimeropsida or Trimerophytopsida (as here),[6] and as an order under the name Trimerophytales.[7]

  • Subphylum †Trimerophytina Banks 1975[8][9]
    • Class †Trimerophytopsida Foster & Gifford 1974 [Trimeropsida Banks 1975; Psilophytopsida Kidston & Lang 1917; Psilophytidae Nemejc 1963]
      • Order †Trimerophytales Banks ex Kasper et al. 1974 [Psilophytales Pia 1924]
        • Family †Trimerophytaceae Banks 1967 [Psilophytaceae Hirmer 1927; Hostinellaceae Pia 1924; Dawsonitaceae Nemejc 1963]
          • Genus †Dawsonites Nemejc 1963
          • Genus †Hostinella Barrande ex Stur 1882
          • Genus †Oocampsa Andrews, Gensel & Kasper 1975
          • Genus †Euphyllophyton Hao & Beck
          • Genus †Pauthecophyton Xue et al. 2012
          • Genus †Psilophyton Dawson 1859 emend. Hueber & Banks 1967
          • Genus †Trimerophyton Hopping 1956

See also


  1. ^ Crane, P.R.; Herendeen, P. & Friis, E.M. (2004), "Fossils and plant phylogeny", American Journal of Botany, 91 (10): 1683–99, doi:10.3732/ajb.91.10.1683, PMID 21652317
  2. ^ Banks, H.P. (1968), "The early history of land plants", in Drake, E.T. (ed.), Evolution and Environment: A Symposium Presented on the Occasion of the 100th Anniversary of the Foundation of Peabody Museum of Natural History at Yale University, New Haven, Conn.: Yale University Press, pp. 73–107, cited in Banks, H.P. (1980), "The role of Psilophyton in the evolution of vascular plants", Review of Palaeobotany and Palynology, 29: 165–176, doi:10.1016/0034-6667(80)90056-1
  3. ^ Banks, H.P. (1975), "Reclassification of Psilophyta", Taxon, 24: 401–413, doi:10.2307/1219491
  4. ^ McNeill, J.; Barrie, F.R.; Buck, W.R.; Demoulin, V.; Greuter, W.; Hawksworth, D.L.; Herendeen, P.S.; Knapp, S.; Marhold, K.; Prado, J.; Prud'homme Van Reine, W.F.; Smith, G.F.; Wiersema, J.H.; Turland, N.J. (2012), International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011, Regnum Vegetabile 154 (electronic ed.), Vienna: A.R.G. Gantner Verlag KG, retrieved 2014-07-02, Article 16.4
  5. ^ Taylor, T.N.; Taylor, E.L. & Krings, M. (2009), Paleobotany, The Biology and Evolution of Fossil Plants (2nd ed.), Amsterdam; Boston: Academic Press, ISBN 978-0-12-373972-8, p. 227
  6. ^ See, e.g., Berry, C.M. & Fairon-Demaret, M. "The Middle Devonian Flora Revisited". In Gensel & Edwards (2001), pp. 120–139.
  7. ^ Banks, H.P. (1970), Evolution and Plants of the Past, London: Macmillan Press, ISBN 978-0-333-14634-7, p. 57
  8. ^ Novíkov & Barabaš-Krasni (2015). "Modern plant systematics". Liga-Pres: 685. doi:10.13140/RG.2.1.4745.6164. ISBN 978-966-397-276-3.
  9. ^ "Part 2- Plantae (starting with Chlorophycota)". Collection of genus-group names in a systematic arrangement. Retrieved 30 June 2016.


  • Gensel, P.G. & Edwards, D., eds. (2001), Plants invade the Land : Evolutionary & Environmental Perspectives, New York: Columbia University Press, ISBN 978-0-231-11161-4

Cyanidiaceae is a family of red algae, one of two families in the Division Cyanidiophytina.


Cyanidiophytina is a subdivision of red algae.In older texts it was described as an order "Cyanidiales". It was granted division status in the Saunders and Hommersand 2004 classification (as "Cyanidophyta"), but was only elevated to subdivision Cyanidiophytina in the Yoon et al. classification of 2006.


The Embryophyta, or land plants, are the most familiar group of green plants that form vegetation on earth. Embryophyta is a clade within the Phragmoplastophyta, a larger clade that also includes several green algae groups (including the Charophyceae and Coleochaetales), and within this large clade the embryophytes are sister to the Zygnematophyceae/Mesotaeniaceae and consist of the bryophytes plus the polysporangiophytes. Living embryophytes therefore include hornworts, liverworts, mosses, ferns, lycophytes, gymnosperms and flowering plants. The Embryophyta are informally called land plants because they live primarily in terrestrial habitats, while the related green algae are primarily aquatic. Embryophytes are complex multicellular eukaryotes with specialized reproductive organs. The name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte. With very few exceptions, embryophytes obtain their energy by photosynthesis, that is by using the energy of sunlight to synthesize their food from carbon dioxide and water.


The euphyllophytes are a clade of plants within the tracheophytes (the vascular plants). The group may be treated as an unranked clade, a division under the name Euphyllophyta or a subdivision under the name Euphyllophytina. The euphyllophytes are characterized by the possession of true leaves ("megaphylls"), and comprise one of two major lineages of extant vascular plants. As shown in the cladogram below, the euphyllophytes have a sister relationship to the lycopodiophytes or lycopsids. Unlike the lycopodiophytes, which consist of relatively few presently living or extant taxa, the euphyllophytes comprise the vast majority of vascular plant lineages that have evolved since both groups shared a common ancestor more than 400 million years ago. The euphyllophytes consist of two lineages, the spermatophytes or seed plants such as flowering plants (angiosperms) and gymnosperms (conifers and related groups), and the monilophytes or ferns, as well as a number of extinct fossil groups. Fossils of lignophytes from early Devonian shows that woody plants were present at least 400 million years ago, a time period when all known plants were small and herbaceous. Because wood evolved long before shrubs and trees, the theory is that its original purpose was for water transport, and that it was only used for mechanical support later. The division of the extant tracheophytes into three monophyletic lineages is supported in multiple molecular studies. Other researchers argue that phylogenies based solely on molecular data without the inclusion of carefully evaluated fossil data based on whole plant reconstructions, do not necessarily completely and accurately resolve the evolutionary history of groups like the euphyllophytes.The following cladogram shows one view of the evolutionary relationships among the taxa described above.

An updated phylogeny of both living and extinct Euphyllophytes with plant taxon authors from Anderson, Anderson & Cleal 2007 and some clade names from Pelletier 2012.


Galdieriaceae is a family of red algae, one of two families in the order Cyanidiales.


Horneophytopsida is a class of extinct plants which consisted of branched stems without leaves, true roots or vascular tissue, found from the Late Silurian to the Early Devonian (around 430 to 390 million years ago). They are the simplest known polysporangiophytes, i.e. plants with sporophytes bearing many spore-forming organs (sporangia) on branched stems. They were formerly classified among the rhyniophytes, but it was later found that some of the original members of the group had simple vascular tissue and others did not.In 2004, Crane et al. published a cladogram for the polysporangiophytes in which the Horneophytopsida are shown as the sister group of all other polysporangiophytes. One other former rhyniophyte, Aglaophyton, is also placed outside the tracheophyte clade, as it did not possess true vascular tissue (in particular did not have tracheids), although its conducting tissue is more complex than that of the Horneophytopsida.


Hostinella is a form genus, used for bare dichotomously branching stems (axes) which have not been found in association with spore-forming organs or sporangia and so cannot be assigned to a more precise genus or species. Specimens assigned to this genus have been found in Bathurst Island, Canada, in beds of Upper Silurian age (around 430 to 420 million years ago), where the stems are approximately 1.2 mm in diameter; and in Lower Devonian Senni beds (from around 420 to 390 million years ago) where the axes have a straited external appearance and contain xylem with tracheids (diameter: 40 µm).It is known to co-occur with Krithodeophyton.


The Division Lycopodiophyta (sometimes called lycophyta or lycopods) is a tracheophyte subgroup of the Kingdom Plantae. It is one of the oldest lineages of extant (living) vascular plants and contains extinct plants like Baragwanathia that have been dated from the Silurian (ca. 425 million years ago). Members of Lycopodiophyta were some of the dominating plant species of the Carboniferous period. These species reproduce by shedding spores and have macroscopic alternation of generations, although some are homosporous while others are heterosporous. Most members of Lycopodiophyta bear a protostele, and the sporophyte generation is dominant. They differ from all other vascular plants in having microphylls, leaves that have only a single vascular trace (vein) rather than the much more complex megaphylls found in ferns and seed plants.


Lycopodiopsida is a class of herbaceous vascular plants known as the clubmosses and firmosses. They have dichotomously branching stems bearing simple leaves called microphylls and reproduce by means of spores borne in sporangia at the bases of the leaves. Traditionally, the group also included the spikemosses (Selaginella and relatives) and the quillworts (Isoetes and relatives) but because these groups have leaves with ligules and reproduce using spores of two different sizes, both are now placed into another class, Isoetopsida that also includes the extinct Lepidodendrales. These groups, together with the horsetails are often referred to informally as fern allies.

The class Lycopodiopsida as interpreted here contains a single living order, the Lycopodiales, and a single extinct order, the Drepanophycales.


Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that terminate in sporangia. The name literally means many sporangia plant. The clade includes all land plants (embryophytes) except for the bryophytes (liverworts, mosses and hornworts) whose sporophytes are normally unbranched, even if a few exceptional cases occur. While the definition is independent of the presence of vascular tissue, all living polysporangiophytes also have vascular tissue, i.e., are vascular plants or tracheophytes. Fossil polysporangiophytes are known that have no vascular tissue, and so are not tracheophytes.


The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the gymnosperms. They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle Devonian order the Aneurophytales, with forms such as Protopteridium, in which the vegetative organs consisted of relatively loose clusters of axes. Tetraxylopteris is another example of a genus lacking leaves. In more advanced aneurophytaleans such as Aneurophyton these vegetative organs started to look rather more like fronds, and eventually during Late Devonian times the aneurophytaleans are presumed to have given rise to the pteridosperm order, the Lyginopteridales. In Late Devonian times, another group of progymnosperms gave rise to the first really large trees known as Archaeopteris.

Other characteristics:

Vascular cambium with unlimited growth potential is present as well as xylem and phloem.

Ancestors of the earliest seed plants as well as the first true trees.

Strong monopodial growth is exhibited.

Some were heterosporous but others were homosporous.


Psilophyton is a genus of extinct vascular plants. Described in 1859, it was one of the first fossil plants to be found which was of Devonian age (about 420 to 360 million years ago). Specimens have been found in northern Maine, USA; Gaspé Bay, Quebec and New Brunswick, Canada; the Czech Republic; and Yunnan, China. Plants lacked leaves or true roots; spore-forming organs or sporangia were borne on the ends of branched clusters. It is significantly more complex than some other plants of comparable age (e.g. Rhynia) and is thought to be part of the group from within which the modern ferns and seed plants evolved.


A pteridophyte is a vascular plant (with xylem and phloem) that reproduces using spores. Because pteridophytes produce neither flowers nor seeds, they are also referred to as "cryptogams", meaning that their means of reproduction is hidden. The pteridophytes include the ferns, horsetails, and the lycophytes (clubmosses, spikemosses, and quillworts). These are not a monophyletic group because ferns and horsetails are more closely related to seed plants than to the lycophytes. Therefore, "Pteridophyta" is no longer a widely accepted taxon, although the term pteridophyte remains in common parlance, as do pteridology and pteridologist as a science and its practitioner, to indicate lycophytes and ferns as an informal grouping, such as the International Association of Pteridologists and the Pteridophyte Phylogeny Group.


Streptophyta, informally the streptophytes (from the Greek strepto, for twisted, i.e., the morphology of the sperm of some members), is a clade of plants. The composition of the clade varies considerably between authors, but the definition employed here includes land plants and all green algae except the Chlorophyta and possibly the more basal Mesostigmatophyceae, Chlorokybophyceae, and Spirotaenia.

Early land flora
Related links
The first...?
Enigmatic taxa
Sister taxa
(red algae)
(green algae,
& land plants)


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