Lycophyte

Last updated

Lycophyte
Temporal range: 428–0  Ma
Ꞓ
O
S
D
C
P
T
J
K
Pg
N
Silurian [1] to recent
Lycophyta.png
Collage of modern lycophytes. Upper left: Lycopodium clavatum (Lycopodiales, Lycopodioideae) Lower left: Huperzia serrata (Lycopodiales, Huperzioideae) Top right: Isoetes japonica (Isoetales) Right centre: Selaginella tamariscina Lower right: Selaginella remotifolia Selaginellales
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Lycophytes
Classes

The lycophytes, when broadly circumscribed, are a group of vascular plants that include the clubmosses. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest lineages of extant (living) vascular plants; the group contains extinct plants that have been dated from the Silurian (ca. 425 million years ago). [2] [3] Lycophytes were some of the dominating plant species of the Carboniferous period, and included the tree-like Lepidodendrales, some of which grew over 40 metres (130 ft) in height, although extant lycophytes are relatively small plants. [4]

Contents

The scientific names and the informal English names used for this group of plants are ambiguous. For example, "Lycopodiophyta" and the shorter "Lycophyta" as well as the informal "lycophyte" may be used to include the extinct zosterophylls or to exclude them.

Description

Lycophytes reproduce by spores and have alternation of generations in which (like other vascular plants) the sporophyte generation is dominant. Some lycophytes are homosporous while others are heterosporous. [5] When broadly circumscribed, the lycophytes represent a line of evolution distinct from that leading to all other vascular plants, the euphyllophytes, such as ferns, gymnosperms and flowering plants. They are defined by two synapomorphies: lateral rather than terminal sporangia (often kidney-shaped or reniform), and exarch protosteles, in which the protoxylem is outside the metaxylem rather than vice versa. The extinct zosterophylls have at most only flap-like extensions of the stem ("enations") rather than leaves, whereas extant lycophyte species have microphylls, leaves that have only a single vascular trace (vein), rather than the much more complex megaphylls of other vascular plants. The extinct genus Asteroxylon represents a transition between these two groups: it has a vascular trace leaving the central protostele, but this extends only to the base of the enation. [6] See § Evolution of microphylls.

Zosterophylls and extant lycophytes are all relatively small plants, but some extinct species, such as the Lepidodendrales, were tree-like, and formed extensive forests that dominated the landscape and contributed to the formation of coal. [6]

Taxonomy

Classification

In the broadest circumscription of the lycophytes, the group includes the extinct zosterophylls as well as the extant (living) lycophytes and their closest extinct relatives. The names and ranks used for this group vary considerably. Some sources use the names "Lycopodiophyta" or the shorter "Lycophyta" to include zosterophylls as well as extant lycophytes and their closest extinct relatives, [7] while others use these names to exclude zosterophylls. [8] [6] The name "Lycopodiophytina" has also been used in the inclusive sense. [9] [10] English names, such as "lycophyte", "lycopodiophyte" or "lycopod", are similarly ambiguous, and may refer to the broadly defined group or only to the extant lycophytes and their closest extinct relatives.

The consensus classification produced by the Pteridophyte Phylogeny Group classification in 2016 (PPG I) places all extant (living) lycophytes in the class Lycopodiopsida. [11] There are around 1,290 to 1,340 such species. [12] [13] [11] For more information on the classification of extant lycophytes, see Lycopodiopsida § Classification.

Phylogeny

A major cladistic study of land plants was published in 1997 by Kenrick and Crane. [1] In 2004, Crane et al. published some simplified cladograms, based on a number of figures in Kenrick and Crane (1997). Their cladogram for the lycophytes is reproduced below (with some branches collapsed into 'basal groups' to reduce the size of the diagram). [14]

 panlycophyte 
 † basal groups 

Cooksonia  cambrensis, Renalia, Sartilmania, Uskiella, Yunia

lycophytes
       

†  Hicklingia

 †basal groups 

Adoketophyton , Discalis , Distichophytum (=Rebuchia), Gumuia , Huia , Zosterophyllum  myretonianum, Z. llanoveranum, Z. fertile

 †'core'  zosterophylls  

Zosterophyllum divaricatum, Tarella , Oricilla , Gosslingia , Hsua, Thrinkophyton , Protobarinophyton , Barinophyton  obscurum, B. citrulliforme, Sawdonia , Deheubarthia , Konioria , Anisophyton , Serrulacaulis , Crenaticaulis

 †basal groups 

Nothia , Zosterophyllum  deciduum

  lycopsids  

extant and extinct members

In this view, the "zosterophylls" comprise a paraphyletic group, ranging from forms like Hicklingia , which had bare stems, [15] to forms like Sawdonia and Nothia , whose stems are covered with unvascularized spines or enations. [16] [17] The genus Renalia illustrates the problems in classifying early land plants. It has characteristics both of the non-lycophyte rhyniophytes – terminal rather than lateral sporangia – and of the zosterophylls – kidney-shaped sporangia opening along the distal margin. [18]

A rather different view is presented in a 2013 analysis by Hao and Xue. Their preferred cladogram shows the zosterophylls and associated genera basal to both the lycopodiopsids and the euphyllophytes, so that there is no clade corresponding to the broadly defined group of lycophytes used by other authors. [19]

 tracheophytes 
         

 basal groups 

 
 

Adoketophyton

Zosterophyllopsida   

 

Lycopsida

 

 basal groups 

Yunia , Dibracophyton

euphyllophytes

 "lycophytes" of other authors

Some extinct orders of lycophytes fall into the same group as the extant orders. Different sources use varying numbers and names of the extinct orders. The following phylogram shows a likely relationship between some of the proposed Lycopodiopsida orders.[ citation needed ]

 Lycopodiopsida 

Evolution of microphylls

Suggested evolution of microphylls: (1) Sawdonia (2) Asteroxylon (3) Leclercqia Microphyll evolution omygod.svg
Suggested evolution of microphylls: (1) Sawdonia (2) Asteroxylon (3) Leclercqia

Within the broadly defined lycophyte group, species placed in the class Lycopodiopsida are distinguished from species placed in the Zosterophyllopsida by the possession of microphylls. Some zosterophylls, such as the Devonian Zosterophyllum myretonianum , had smooth stems (axes). Others, such as Sawdonia ornata , had flap-like extensions on the stems ("enations"), but without any vascular tissue. Asteroxylon , identified as an early lycopodiopsid, had vascular traces that extended to the base of the enations. Species in the genus Leclercqia had fully vascularized microphylls. These are considered to be stages in the evolution of microphylls. [20]

Related Research Articles

<span class="mw-page-title-main">Lycopodiopsida</span> Class of vascular plants

Lycopodiopsida is a class of vascular plants known as lycopods, lycophytes or other terms including the component lyco-. Members of the class are also called clubmosses, firmosses, spikemosses 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 (Lepidodendrales) formed huge forests that dominated the landscape and contributed to coal deposits.

In plant anatomy and evolution a microphyll is a type of plant leaf with one single, unbranched leaf vein. Plants with microphyll leaves occur early in the fossil record, and few such plants exist today. In the classical concept of a microphyll, the leaf vein emerges from the protostele without leaving a leaf gap. Leaf gaps are small areas above the node of some leaves where there is no vascular tissue, as it has all been diverted to the leaf. Megaphylls, in contrast, have multiple veins within the leaf and leaf gaps above them in the stem.

<span class="mw-page-title-main">Pteridophyte</span> Group of plants that reproduce by spores

A pteridophyte is a vascular plant that reproduces by means of spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden.

<span class="mw-page-title-main">Zosterophyll</span> Group of extinct land plants that first appeared in the Silurian period

The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta or Zosterophyta and the class or plesion Zosterophyllopsida or Zosteropsida. They were among the first vascular plants in the fossil record, and had a world-wide distribution. They were probably stem-group lycophytes, forming a sister group to the ancestors of the living lycophytes. By the late Silurian a diverse assemblage of species existed, examples of which have been found fossilised in what is now Bathurst Island in Arctic Canada.

<i>Asteroxylon</i> Extinct genus of spore-bearing plants

Asteroxylon is an extinct genus of vascular plants of the Division Lycopodiophyta known from anatomically preserved specimens described from the famous Early Devonian Rhynie chert and Windyfield chert in Aberdeenshire, Scotland. Asteroxylon is considered a basal member of the Lycopsida.

<span class="mw-page-title-main">Drepanophycales</span> Extinct order of spore-bearing plants

Drepanophycales is an order of extinct lycophyte plants of Late Silurian to Late Devonian age, found in North America, China, Russia, Europe, and Australia. Sometimes known as the Asteroxylales or Baragwanathiales.

<i>Zosterophyllum</i> Extinct genus of spore-bearing plants

Zosterophyllum was a genus of Silurian-Devonian vascular land plants with naked branching axes on which usually kidney-shaped sporangia were arranged in lateral positions. It is the type genus for the group known as zosterophylls, thought to be part of the lineage from which modern lycophytes evolved. More than 20 species have been described.

Crenaticaulis was an early genus of slender, dichotomously branching, leafless land plants, known from the Devonian period and first described in 1969. They were probably allied to the zosterophylls, and are assigned to subdivision Zosterophyllophytina, or class Zosterophyllopsida. They bore branches and scalariform tracheids.

<span class="mw-page-title-main">Polysporangiophyte</span> Spore-bearing plants with branched sporophytes

Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that bear sporangia. The name literally means 'many sporangia plant'. The clade includes all land plants (embryophytes) except for the bryophytes 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. Extinct polysporangiophytes are known that have no vascular tissue and so are not tracheophytes.

<span class="mw-page-title-main">Sawdoniales</span> Extinct order of spore-bearing plants

The Sawdoniales are an order or plesion of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and share an ancestor with the living lycophytes. The group has been divided up in various ways. In their major cladistic study of early land plants, Kenrick and Crane placed most of the zosterophylls in the Sawdoniales.

Sawdonia is an extinct genus of early vascular plants, known from the Upper Silurian to the Lower Carboniferous. Sawdonia is best recognized by the large number of spikes (enations) covering the plant. These are vascular plants that do not have vascular systems in their enations. The first species of this genus was described in 1859 by Sir J. William Dawson and, was originally attributed to the genus Psilophyton. He named this plant Psilophyton princeps. In 1971 Francis Hueber proposed a new genus for this species due to its "Divergent technical characters from the generic description for Psilophyton." The holotype used for description is Dawson Collection Number 48, pro parte, Museum Specimen Number 3243. Sir J. William Dawson Collection, Peter Redpath Museum, McGill University, Montreal, Quebec, Canada.

Psilophytopsida is a now obsolete class containing one order, Psilophytales, which was previously used to classify a number of extinct plants which are now placed elsewhere. The class was established in 1917, under the name Psilophyta, with only three genera for a group of fossil plants from the Upper Silurian and Devonian periods which lack true roots and leaves, but have a vascular system within a branching cylindrical stem. The living Psilotaceae, the whisk-ferns, were sometimes added to the class, which was then usually called Psilopsida. This classification is no longer in use.

<i>Yunia</i> Extinct genus of spore-bearing plants

Yunia is a genus of extinct vascular plants from the Early Devonian. It was first described from the Posongchong Formation of Yunnan, China. The leafless plant consisted of spiny stems, some 2 to 5 cm wide, which branched dichotomously at wide angles in a cruciate arrangement. Each stem contained vascular tissue with one or two strands of protoxylem. The spore-forming organs (sporangia) were elongated and borne on short stalks. The spores had a relatively smooth sculptural pattern and were trilete.

Hicklingia is a genus of extinct plants of the Middle Devonian. Compressed specimens were first described in 1923 from the Old Red Sandstone of Scotland. Initially the genus was placed in the "rhyniophytes", but this group is defined as having terminal sporangia, and later work showed that the sporangia of Hicklingia were lateral rather than strictly terminal, so that it is now regarded as having affinities with the zosterophylls.

Huia is a genus of extinct vascular plants of the Early Devonian. The genus was first described in 1985 based on fossil specimens from the Posongchong Formation, Wenshan district, Yunnan, China.

<i>Adoketophyton</i> Extinct genus of spore-bearing plants

Adoketophyton is a genus of extinct vascular plants of the Early Devonian. The plant was first described in 1977 based on fossil specimens from the Posongchong Formation, Wenshan district, Yunnan, China. These were originally named Zosterophyllum subverticillatum; later the species was transferred to a new genus as Adoketophyton subverticillatum. One cladistic analysis suggested that it is a lycophyte, related to the zosterophylls. Other researchers regard its placement within the vascular plants as uncertain.

<i>Nothia aphylla</i> Extinct species of spore-bearing plant

Nothia was a genus of Early Devonian vascular plants whose fossils were found in the Rhynie chert in Scotland. It had branching horizontal underground stems (rhizomes) and leafless aerial stems (axes) bearing lateral and terminal spore-forming organs (sporangia). Its aerial stems were covered with small 'bumps' (emergences), each bearing a stoma. It is one of the best described early land plants. Its classification remains uncertain, although it has been treated as a zosterophyll. There is one species, Nothia aphylla.

Protobarinophyton was a genus of Silu-Devonian land plant with branching axes. It is placed in a group of early vascular plants (tracheophytes), the barinophytes, a group that has been given various ranks and scientific names.

Gosslingiales is an order of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and share an ancestor with the living lycophytes. The group has been divided up in various ways. Hao and Xue in 2013 used the presence or absence of terminal sporangia as a major dividing feature. The order Zosterophyllales was used for species with terminal as well as lateral sporangia, which were considered to have determinate growth, with their sporangia generally being arranged in spikes. The paraphyletic order Gosslingiales was used for species without terminal sporangia, which were considered to have indeterminate growth, with fertile branches generally circinate. Species assignable to the Gosslingiales made up about 9% of all confirmed species in the Early Devonian flora.

The barinophytes are a group of extinct vascular plants (tracheophytes). Their relationship with other vascular plants is unclear. They have been treated as the separate class Barinophytopsida, the order Barinophytales of uncertain class and as a family or clade Barinophytaceae within the zosterophylls. They have also been considered to be possible lycopodiopsids.

References

  1. 1 2 Kenrick, Paul; Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press. pp. 339–340. ISBN   978-1-56098-730-7.
  2. ↑ Rickards, R.B. (2000). "The age of the earliest club mosses: the Silurian Baragwanathia flora in Victoria, Australia". Geological Magazine. 137 (2): 207–209. Bibcode:2000GeoM..137..207R. doi:10.1017/s0016756800003800. S2CID   131287538.
  3. ↑ McElwain, Jenny C.; Willis, K. G.; Willis, Kathy; McElwain, J. C. (2002). The evolution of plants. Oxford [Oxfordshire]: Oxford University Press. ISBN   978-0-19-850065-0.
  4. ↑ Ranker, T. A.; Hauler, C. H. (2008). Biology and evolution of ferns and lycophytes. Cambridge: Cambridge University Press.
  5. ↑ Eichhorn, Evert, and Raven (2005). Biology of Plants, Seventh Edition. 381-388.
  6. 1 2 3 Mauseth, James D. (2014). Botany : An introduction to Plant Biology (5th ed.). Burlington, MA: Jones & Bartlett Learning. ISBN   978-1-4496-6580-7.
  7. ↑ Doweld, Alexander B. (2017). "(2499) Proposal to conserve the name Zosterophyllaceae against Sciadophytaceae (Fossil Lycopodiophyta: Zosterophyllopsida)". Taxon. 66 (1): 207–208. doi: 10.12705/661.27 .
  8. ↑ 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.
  9. ↑ Kenrick, Paul & Crane, Peter R. (1997a). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D.C.: Smithsonian Institution Press. ISBN   978-1-56098-730-7.
  10. ↑ Kenrick, Paul & Crane, Peter R. (1997b). "The origin and early evolution of plants on land". Nature. 389 (6646): 33–39. Bibcode:1997Natur.389...33K. doi:10.1038/37918. S2CID   3866183.
  11. 1 2 PPG I (2016). "A community-derived classification for extant lycophytes and ferns". Journal of Systematics and Evolution. 54 (6): 563–603. doi: 10.1111/jse.12229 . S2CID   39980610.
  12. ↑ Callow, R.S. & Cook, Laurence Martin (1999). Genetic and evolutionary diversity: the sport of nature. Cheltenham: S. Thornes. p. 8. ISBN   978-0-7487-4336-0.
  13. ↑ Christenhusz, M. J. M., M.J.M. & Byng, J.W. (2016). "The number of known plants species in the world and its annual increase". Phytotaxa. 261 (3): 201–217. doi: 10.11646/phytotaxa.261.3.1 .
  14. ↑ Crane, P.R.; Herendeen, P. & Friis, E.M. (2004). "Fossils and plant phylogeny". American Journal of Botany. 91 (10): 1683–1699. doi: 10.3732/ajb.91.10.1683 . PMID   21652317. S2CID   8493380.
  15. ↑ Edwards, D. (1976). "The systematic position of Hicklingia edwardii Kidston and Lang". New Phytologist. 76: 173–181. doi: 10.1111/j.1469-8137.1976.tb01449.x .
  16. ↑ Taylor, Taylor & Krings (2009), p. 253.
  17. ↑ Kerp, H.; Hass, M.H. & Mosbrugger, V. (2001). "New Data on Nothia aphylla Lyon 1964 ex El-Saadawy et Lacey 1979, a Poorly Known Plant from the Lower Devonian Rhynie Chert". In Gensel, P.G. & Edwards, D. (eds.). Plants invade the Land : Evolutionary & Environmental Perspectives. New York: Columbia University Press. pp. 52–82. ISBN   978-0-231-11161-4.
  18. ↑ Taylor, Taylor & Krings (2009), p. 250.
  19. ↑ Hao, Shougang & Xue, Jinzhuang (2013). The early Devonian Posongchong flora of Yunnan: a contribution to an understanding of the evolution and early diversification of vascular plants. Beijing: Science Press. Fig. 6.8, p. 246. ISBN   978-7-03-036616-0.
  20. ↑ Taylor, Taylor & Krings (2009), p. 267ff.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.