These organisms all exhibit sporophytes that remain attached to, and nutritionally dependent on, the gametophyte generation. For the most part, they lack specialized water-conducting tissue, yet remain amazingly good at enduring dry conditions.
Moss and liverwort gametophytes vary in how sexual function is expressed. Sex chromosomes, and thus separate male and female gametophytes, are found in some genera (in some instances males are dwarf plants that grow resting on the female ones). In other genera both antheridia and archegonia are produced on the same gametophyte.
sp.; the brown, stalked structures are the spore-containing capsules of
the sporophyte (the capsules would be approx. 1-2 mm in diameter). It
is the green, leafy gametophyte of Sphagnum, however, that
is of enormous ecological, economic, and scientific importance worldwide
because of the ion-exchange characteristics of the leaves both living
Photo: M. Ferguson © 1997 Royal Ontario Museum
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Gametophytes of the thallose liverwort Marchantia (note wooden match for scale above). At the far left, antheridiophores (dark) and archegoniophores (pink). Below left, section through an antheridiophore of Marchantia, showing antheridia. Archegoniophores develop tiny sporophytes on their undersides after the egg in an archegonium is fertilized (left).
Liverworts include not only thalloid taxa like Marchantia and its relatives, but also leafy ones, and ones that appear to be intermediate between these two forms.
Photo: far left, M. Ferguson © 1997 Royal Ontario Museum; left, prepared slide, © 2009 Royal Ontario Museum; above, T. A. Dickinson © 1996 T. A. Dickinson; bottom left, prepared slide, © 2009 Royal Ontario Museum.
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Dendroceros sp.; the crispy thallose structures growing on the soil surface are the
gametophytes. The conspicuous upright, linear green sporophytes (approx.
2-3 cm long) consist of nothing but one long sporangium that can be seen
to be dehiscing from the tip downwards - Jamaica
Photo: T. A. Dickinson © 1996 T. A. Dickinson
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For more information, visit these sites: "What is a Bryophyte?" and the BBS Image Galleries 1, 2, 3, and 4, from the British Bryological Society; The World of Mosses (with Robert Muma's "A Graphic Guide to Ontario Mosses," and many of his paintings, among other things); the SIUC Bryophyte Website; or the UBC Bryology site. You may also wish to consult the newly published second edition of Bryophyte Biology, edited by Goffinet and Shaw (Cambridge University Press, 2009). Or, you can download a chapter on the morphology of mosses from the Flora North America website.
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