Write An Essay On Pteridophytes Characteristics

The Pteridophytes comprise of the lower vascular plants (Trachaeophyta) which show distinctly vascular, independent sporophytic plants arising from embryos (Embryophyta or Cormophyta) which are not enclosed within any ‘seed’ structure. These alternate with independent gametophytes which are almost bryophytic in appearance and bear antheridia and archegonia (Archegoniatae).

These lower vascular plants are called the Pteridophytes or the Pteridophyta. Although numerically much below the Bryophytes (there are 23,000 living species in about 900 genera of Bryophytes against about 10,500 species in some 400 genera of living and fossil Pteridophytes) the Pteridophytes claim a special position as the first land plants forming forests.

But the idea of the relative position of this group Pteridophyta within the Plant Kingdom has greatly changed in recent days.

The artificial concept of dividing the Plant Kingdom into the Cryptogams and the Phane­rogams persisted throughout the 19th century but was practically abandoned in the twentieth. Even during the 19th century we find abandonment of the idea of con­sidering the Cryptogams as a group.

Auguste Pyramos de Candolle, who coined the term‘Taxonomy’ (1813) divided the Plant Kingdom into the Cellulares (Thallophyta and Bryophyta) and the Vasculares (Vascular Plants) in 1819.

Thus, de Candolle was the first to recognise that the Pteridophytes should rather be linked with the higher plants than with the artificial Linnaen group of Cryptogams.

Stephen Endlicher divided the Plant Kingdom into Thallophyta and Cormophyta raising the Bryophytes also to the higher Cormophytes. In the latter part of the 19th century, A.

Engler also supported Endlicher and stated that it was much better to divide the Plant Kingdom into two groups: Thallophyta and Embryophyta.

Our concept of both the Thallophyta and the Embryophyta has undergone much change during the 20th century.

One idea had been to consider the Pteridophyta as a division of the Plant Kingdom parallel to the three other divisions—Thallophyta, Bryophyta and Spermophyta. Jeffrey (1902) first proposed that the original units be aban­doned and the vascular plants be divided into two stocks the Lycopsida (Lycopods and Equisetums) and the Pteropsida (Ferns, Gymnosperms and Angiosperms).

Bessey (1911) divided the whole Plant Kingdom directly into 14 phyla, the 9th, 10th and 11th of which comprise of the Pteridophytes.

Engler, in the 1936 edition of the Syllabus similarly divides the Plant Kingdom directly into 14 Abteilungen (Divi­sions) the first 12 of which are Thallophytes, the 13th is Archegoniatae (or Embryo­phyta Asiphonogama) and the 14th Embryophyta Siphonogama (Gymnosperms and Angiosperms).

The Archegoniatae are again divided into two subdivisions (Unterab- teilungen): Bryophyta and Pteridophyta.

In 1935, Sinnott proposed the term ‘Tra­chaeophyta’ to include all the Vascular Plants. Tippo (1942) suggested that the Plant Kingdom be divided into two subkingdoms Thallophyta and Embryophyta and the latter be divided into two phyla—Bryophyta and Trachaeophyta.

Takhtajan (1950) coined the term ‘Telemophyta’ to rename the Embryophyta in view of the Telome Theory. Bold (1957) suggested dividing the Plant Kingdom into three subkingdoms Thallophyta, Bryophyta and Trachaeophyta.

Consideration of the Trachaeophyta as a distinct group emphasises the most important character acquired by the land plants—the vascular bundles. The Trachaeophytes, no doubt, show certain characters embodying the main trend of evolution since the land habit was acquired. But, this is too vast a group to be considered as a single division as a vast majority of the modern plants are included here.

Moreover, Takhtajan (1953) and others do not think that the Bryophyta should be separated from the Trachaeo­phyta, the former being a possible derivative of the latter. This point has now been emphasised by Cronquist, Takhtajan and Zimmermann (1966).

The living Pteridophytes distinctly show four groups of plants representing four lines of evolution. The first three of these lines—the Psilotums, the Lycopods and the Equisetums—ended blindly. The last—the Ferns-evolved further into the Gym- nosperms and the Angiosperms.

Because of this, Bessey (1911) proposed the abolition of the old taxon Pteridophyta replacing it by three divisions (‘phyla’)— Pteridophyta -proper (ferns), Calamophyta and Lepidophyta.

Since then other divisions have been added, most important of which is the division Psilophyta.

Some systematists have retained Pteridophyta as a division calling the main taxa ‘classes’ (some have called the main taxa ‘phyla’, a term used in Zoology but cannot be retained in Botany according to International Rules of Botanical Nomenclature) while others have deleted the Pteridophyta as a taxon raising the lower taxa themselves into divisions.

A pteridophytesensu lato is a vascular plant (with xylem and phloem) that reproduces via spores, and therefore was a member of the former and now invalid taxonPteridophyta. The term is now used only informally to denominate a fern (monilophyte) or lycophyte. Because pteridophytes produce neither flowers nor seeds, they are also referred to as "cryptogams". 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 now an invalid 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.

Description[edit]

Ferns and lycophytes (pteridophytes) are free-sporing vascular plants that share a unique life cycle with independent gametophyte and sporophyte phases that are frequently discussed together due to common characteristics, including vascular plant apomorphies (e.g., vascular tissue) and land plantplesiomorphies (e.g., spore dispersal and the absence of seeds).

Taxonomy[edit]

Phylogeny[edit]

Of the pteridophytes, ferns account for nearly 90% of the extant diversity. Smith et al. (2006), the first higher-level pteridophyte classification published in the molecular phylogenetic era, considered the ferns as monilophytes, as follows:

where the monilophytes comprise about 9,000 species, including horsetails (Equisetaceae), whisk ferns (Psilotaceae), and all eusporangiate and all leptosporangiate ferns. Historically both lycophytes and monilophytes were grouped together as pteridophytes (ferns and fern allies) on the basis of being spore-bearing ("seed-free"). In Smith's molecular phylogenetic study the ferns are characterised by lateral root origin in the endodermis, usually mesarchprotoxylem in shoots, a pseudoendospore, plasmodialtapetum, and sperm cells with 30-1000 flagella. The term "moniliform" as in Moniliformopses and monilophytes means "bead-shaped" and was introduced by Kenrick and Crane (1997) as a scientific replacement for "fern" (including Equisetaceae) and became established by Pryer et al. (2004). Christenhusz and Chase (2014) in their review of classification schemes provide a critique of this usage, which they discouraged as irrational. In fact the alternative name Filicopsida was already in use. By comparison "lycopod" or lycophyte (club moss) means wolf-plant. The term "fern ally" included under Pteridophyta generally refers to vascular spore-bearing plants that are not ferns, including lycopods, horsetails, whisk ferns and water ferns (Marsileaceae, Salviniaceae and Ceratopteris), and even a much wider range of taxa. This is not a natural grouping but rather a convenient term for non-fern, and is also discouraged, as is eusporangiate for non-leptosporangiate ferns.

However both Infradivision and Moniliformopses are also invalid names under the International Code of Botanical Nomenclature. Ferns, despite forming a monophyleticclade, are formally only considered as four classes (Psilotopsida; Equisetopsida; Marattiopsida; Polypodiopsida), 11 orders and 37 families, without assigning a higher taxonomic rank.

Furthermore, within the Polypodiopsida, the largest grouping, a number of informal clades were recognised, including leptosporangiates, core leptosporangiates, polypods (Polypodiales), and eupolypods (including Eupolypods I and Eupolypods II).

In 2014 Christenhusz and Chase, summarising the known knowledge at that time, treated this group as two separate unrelated taxa in a consensus classification;

  • Lycopodiophyta (lycopods) 1 subclass, 3 orders, each with one family, 5 genera, approx. 1,300 species
  • Polypodiophyta (ferns) 4 sublasses, 11 orders, 21 families, approx. 212 genera, approx. 10,535 species

These subclasses correspond to Smith's four classes, with Ophioglossidae corresponding to Psilotopsida.

The two major groups previously included in Pteridophyta are phylogenetically related as follows:

Subdivision[edit]

Pteridophytes consist of two separate but related classes, whose nomenclature has varied. The terminology used by the Pteridophyte Phylogeny Group (2016) (with some synonyms) is used here:

Classes, subclasses and orders

In addition to these living groups, several groups of pteridophytes are now extinct and known only from fossils. These groups include the Rhyniopsida, Zosterophyllopsida, Trimerophytopsida, the Lepidodendrales and the Progymnospermopsida.

Modern studies of the land plants agree that all pteridophytes share a common ancestor with seed plants. Therefore, pteridophytes do not form a clade but constitute a paraphyletic group.

Ecology[edit]

Just as with seed plants and mosses, the life cycle of pteridophytes involves alternation of generations. This means that a diploid generation (the sporophyte, which produces spores) is followed by a haploid generation (the gametophyte or prothallus, which produces gametes). Pteridophytes differ from mosses and seed plants in that both generations are independent and free-living, although the sporophyte is generally much larger and more conspicuous. The sexuality of pteridophyte gametophytes can be classified as follows:

  • Dioicous: each individual gametophyte is either male (producing antheridia and hence sperm) or female (producing archegonia and hence egg cells).
  • Monoicous: each individual gametophyte produces both antheridia and archegonia and can function both as a male and as a female.
    Protandrous: the antheridia mature before the archegonia (male first, then female).
    Protogynous: the archegonia mature before the antheridia (female first, then male).

These terms are not the same as monoecious and dioecious, which refer to whether a seed plant's sporophyte bears both male and female gametophytes, i. e., produces both pollen and seeds, or just one of the sexes.

See also[edit]

References[edit]

Bibliography[edit]

  • Cantino, Philip D.; Doyle, James A.; Graham, Sean W.; Judd, Walter S.; Olmstead, Richard G.; Soltis, Douglas E.; Soltis, Pamela S.; Donoghue, Michael J. (1 August 2007). "Towards a Phylogenetic Nomenclature of Tracheophyta". Taxon. 56 (3): 822. doi:10.2307/25065865. 
  • Christenhusz, M. J. M.; Zhang, X. C.; Schneider, H. (18 February 2011). "A linear sequence of extant families and genera of lycophytes and ferns"(PDF). Phytotaxa. 19 (1): 7. doi:10.11646/phytotaxa.19.1.2. 
  • Christenhusz, Maarten J.M. & Chase, Mark W. (2014). "Trends and concepts in fern classification". Annals of Botany. 113 (9): 571–594. doi:10.1093/aob/mct299. PMC 3936591. PMID 24532607. 
  • Clark, James; Hidalgo, Oriane; Pellicer, Jaume; Liu, Hongmei; Marquardt, Jeannine; Robert, Yannis; Christenhusz, Maarten; Zhang, Shouzhou; Gibby, Mary; Leitch, Ilia J.; Schneider, Harald (May 2016). "Genome evolution of ferns: evidence for relative stasis of genome size across the fern phylogeny". New Phytologist. 210 (3): 1072–1082. doi:10.1111/nph.13833. 
  • Chase, Mark W. & Reveal, James L. (2009). "A phylogenetic classification of the land plants to accompany APG III". Botanical Journal of the Linnean Society. 161: 122–127. doi:10.1111/j.1095-8339.2009.01002.x. 
  • Gifford, Ernest M.; Foster, Adriance S. (1996). Morphology and evolution of vascular plants (3rd ed.). New York: Freeman. ISBN 0-7167-1946-0. 
  • Kenrick, Paul; Crane, Peter (1996). "Embryophytes: Land plants". Tree of Life Web Project. Retrieved 19 April 2017. 
  • Kenrick, Paul; Crane, Peter R. (4 September 1997). "The origin and early evolution of plants on land"(PDF). Nature. 389: 33–39. doi:10.1038/37918. 
  • Kenrick, Paul; Crane, Peter (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D.C.: Smithsonian Institution Press. ISBN 9781560987291. 
  • Pryer, K. M.; Schuettpelz, E.; Wolf, P. G.; Schneider, H.; Smith, A. R.; Cranfill, R. (1 October 2004). "Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences". American Journal of Botany. 91 (10): 1582–1598. doi:10.3732/ajb.91.10.1582. 
  • Pteridophyte Phylogeny Group (November 2016). "A community-derived classification for extant lycophytes and ferns". Journal of Systematics and Evolution. 54 (6): 563–603. doi:10.1111/jse.12229. 
  • Ranker, Tom A.; Haufler, Christopher H. (2008). Biology and Evolution of Ferns and Lycophytes. Cambridge University Press. ISBN 978-0-521-87411-3. 
  • Raven, Peter H.; Evert, Ray F.; Eichhorn, Susan E. (2005). Biology of plants (7th ed.). New York, NY: Freeman and Company. ISBN 0-7167-1007-2. 
  • Schneider, Harald; Schuettpelz, Eric (November 2016). "Systematics and evolution of lycophytes and ferns". Journal of Systematics and Evolution. 54 (6): 561–562. doi:10.1111/jse.12231. 
  • Smith, Alan R.; Kathleen M. Pryer; Eric Schuettpelz; Petra Korall; Harald Schneider; Paul G. Wolf (2006). "A classification for extant ferns"(PDF). Taxon. 55 (3): 705–731. doi:10.2307/25065646. JSTOR 25065646. 
  • Pteridophyte Phylogeny Group (November 2016). "A community-derived classification for extant lycophytes and ferns". Journal of Systematics and Evolution. 54 (6): 563–603. doi:10.1111/jse.12229. 

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