Pteridophyte

The pteridophytes are vascular plants (plants with xylem and phloem) that neither flower nor produce seeds, hence they are called vascular cryptogams. Instead, they reproduce and disperse only via spores.

Pteridophyte classification

They do not form a monophyletic group but consist of two groups:^[1]

• the Lycopodiophyta (club mosses, spike mosses, and quillworts),
• Ferns:
  • Marattioid ferns,
  • Equisetophyta (horsetails),
  • Psilotophyta (whisk ferns) and Ophioglossophyta (adder's tongues and grape ferns),
  • Leptosporangiate ferns (the largest group of ferns).

In addition to these living groups of pteridophytes are several groups now extinct and known only from fossils. These groups include the Rhyniophyta, Zosterophyllophyta, Trimerophytophyta, and the progymnosperms.

Modern studies of the land plants agree that all the pteridophytes share a single common ancestor. However, they are not a clade (monophyletic group) because the seed plants are also descended from within this group—probably close relatives of the progymnosperms.

Pteridophyte sexuality

These plants are generally sporophyte-oriented; that is, the normal plant is the diploid sporophyte, with the only haploid structure being the gametophyte (prothallium) in season. This basic pattern is like that found in the seed plants but with an important exception. Unlike the seed plants, the pteridophytes have a gametophyte stage that is free-living. As a result, pteridophyte sexuality is more complicated than that of the seed plants. There are several basic categories of sexuality in pteridophytes. The terms distinguish between types of gametophyte sexuality:

• Dioicous pteridophytes produce only antheridia (male organs) or archegonia (female organ) on a single gametophyte body.
• Monoicous pteridophytes produce both antheridia and archegonia on the same gametophyte body.

  Protandrous pteridophytes produce the male antheridia first, and then their female archegonia.

  Protogynous pteridophytes produce the archegonia first, followed by the antheridia.

Notice that these terms are not the same as monoecious and dioecious, which refer to whether or not a sporophyte plant bears one or both kinds of gametophyte. Those terms apply only to seed plants.

See also

• Embryophyte
• Plant sexuality

References

1. ^ Schuettpelz, Eric. "Fern Phylogeny Inferred from 400 Leptosporangiate Species and Three Plastid Genes," contained in "The Evolution and Diversification of Epiphytic Ferns." Doctoral dissertation, Duke University. 2007. http://dukespace.lib.duke.edu/dspace/bitstream/10161/181/1/D_Schuettpelz_Eric_a_052007.pdf

• 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.