Pteridophyte

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A pteridophyte sensu lato is a vascular plant (with xylem and phloem) that reproduces via spores, and therefore was a member of the former and now invalid taxon denominated Pteridophyta; the denomination sensu stricto presently only has informal use to denominate a monilophyte (fern) or lycophyte, or simply and only a monilophyte. Because pteridophytes produce neither flowers or seeds, they are also denominated "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.

Classification[edit]

Pteridophytes consist of two separate classes:[1][2]

In addition to these living groups, several groups that are now extinct and known only from fossils are considered pteridophytes. These groups include the Rhyniophyta, Zosterophyllophyta, Trimerophytophyta, and the progymnospermprogymnosperms.[citation needed]

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

Life cycle[edit]

Pteridophyte life cycle

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]

  1. ^ 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. 
  2. ^ Tree of Life web project
  • Gifford, Ernest M. & Foster, Adriance S. (1988). Morphology and Evolution of Vascular Plants, (3rd ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1946-0.
  • Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (2005). Biology of Plants (7th ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1007-2.