BOT 360F - Families of Vascular Plants

Pteridophytes

"Ferns and Fern Allies;" "Vascular Cryptogams"

Pteridophyte life cycle
  Pteridophyte archegonium  

Gametophyte

..."prothallus"
...freeliving, usually photosynthetic, but without vascular tissue, cuticle, and stomates, and hence inconspicuous and small (101 cm), confined to relatively moist situations.
...producing male and female gametangia, i.e. antherida and archegonia, respectively. Male gametes flagellated, female gametes sessile, within archegonium. Fertilization depends upon the availability of a film of liquid water within which sperm can swim to the archegonia (illustrations not to same scale, redrawn from Sporne 1975; images of prepared slides © 2009 Royal Ontario Mueum).
Pteridophyte antheridium fern antheridia fern gametophyte
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Sporophyte

...independent of the gametophyte at maturity, photosynthetic, with vascular tissue, cuticle, and stomates, and hence varying considerably in size (101 - 103 cm) and complexity.
...producing spores in sporangia classified according to their development as eusporangiate or leptosporangiate (compare diagrams above, below). Spores all of one size (homosporous), or of two sizes (large, small; heterosporous).
Matteucia struthiopteris - TRT 443
Leptosporangiate development
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Ecology

...represented today by a variety of growth habits (life forms), hence occupying a wide range of habitats, notwithstanding the dependence on the availability of liquid water for sexual reproduction.
  • aquatic (Marsileales, Salviniales)
  • rhizomatous
  • clumped
  • terrestrial, epiphytic
  • arboreal (Dicksoniaceae; tree ferns)
  • sometimes extremely weedy, e.g. bracken (Pteridium aquilinum)
...as a group, much more abundant and diverse during the latter part of the Paleozoic and the Mesozoic than presently.
...dispersal occurs via spores, of whatever kind, i.e. by single cells however large.

Genetics

...have only recently been examined in light of thinking about the theoretical importance of outcrossing.
  • Work in the 1970s documenting the breeding systems of homosporous ferns has provided an impetus for new questions about gametophyte biology and cytogenetics in these plants
  • Haufler CH (2014) Ever since Klekowski: Testing a set of radical hypotheses revives the genetics of ferns and lycophytes. American Journal of Botany 101: 2036-2042. [Open Access]
  • The life cycle of ferns has also been the subject of revisionary comments about the way it is taught; see Haufler CH, Pryer KM, Schuettpelz E, Sessa EB, Farrar DR, Moran R, Schneller JJ, James E. Watkins J, Windham MD (2016) Sex and the Single Gametophyte: Revising the Homosporous Vascular Plant Life Cycle in Light of Contemporary Research. Bioscience 66: 928-937. [not Open Access, unfortunately]
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Heterospory

...is the production of (two) different kinds of spores; microspores and megaspores.
...megaspore germinates to give rise to female gametophyte; microspore to male gametophyte, in both cases the gametophytes being retained within the spore wall.
...male prothallus reduced to a single antheridium from which varying numbers of motile sperm are released.
...female prothallus develops first by free-nuclear divisions, often while the megaspore is still in the sporangium. Cell walls are then laid down and archegonia and rhizoids develop as the spore wall ruptures.
...fertilization results in development of an embryo sporophyte, initially still within the wall of the megaspore.
...modern examples include Selaginella and Isoetes (Lycopodiophyta), and the water ferns (Marsileales, Salviniales; Polypodiophyta).
Endosporic embryo development
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Please send your comments to tim.dickinson@utoronto.ca; last updated 27-Jan-2017