Bryophyte

Bryophytes are members of the land plants that are non-vascular, meaning that they lack water- and food-conducting strands in their roots (xylem and phloem), or that they are poorly developed. Three of the twelve phyla within the division Bryophyta are the mosses (phylum Bryophyta), liverworts (phylum Hepaticophyta), and hornworts (phylum Anthocerotophyta). Bryophytes have tissues and enclosed reproductive systems, but they neither flower nor produce seeds, reproducing via spores. The ecologically persistent, photosynthetic phase of the life cycle is the haploid, gametophyte generation rather than the diploid sporophyte; bryophyte sporophytes are very short-lived, are attached to and nutritionally dependent on their gametophytes and consist of only an unbranched stalk, or seta, and a single, terminal sporangium (Stotler and Stotler 2005). Bryophytes are widely distributed globally and exhibit significant ecological diversity. They are typically small, herbaceous plants, growing closely packed in mats or cushions on rocks, soil, or as epiphytes on the trunks of trees.

Bryophyte classification

There are three groups, the Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses). Modern studies generally show one of two patterns. In one of these patterns, the liverworts were the first to diverge, followed by the hornworts, while the mosses are the closest living relatives of the vascular plants. In the other pattern, the hornworts were the first to diverge, followed by the vascular plants, while the mosses are the closest living relatives of the liverworts. Originally the three groups were brought together as the three classes of division Bryophyta. However, since the three groups of bryophytes form a paraphyletic group, they now are placed in three separate divisions.

Bryophyte sexuality

The bryophytes are generally gametophyte-oriented; that is, the normal plant is the haploid gametophyte, with the only diploid structure being the sporangium in season. The bryophyte sporophyte remains attached to the gametophyte, and does not become a free-living plant, as in other land plants. As a result, bryophyte sexuality is very different from that of other plants. There are two basic categories of sexuality in bryophytes:

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

Some bryophyte species may be either monoicous or dioicous depending on environmental conditions. Other species grow exclusively with one type of sexuality.

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
• Marchantiophyta (liverworts)
• Anthocerotophyta (hornworts)
• Bryophyta (mosses)
• Plant sexuality

References

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• Chopra, R. N. & Kumra, P. K. (1988). Biology of Bryophytes. New York: John Wiley & Sons. ISBN 0-470-21359-0.
• Crum, Howard (2001). Structural Diversity of Bryophytes. Ann Arbor: University of Michigan Herbarium. ISBN 0-9620733-4-2.
• Goffinet, Bernard. (2000). Origin and phylogenetic relationships of bryophytes. In A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology, pp. 124-149. Cambridge: Cambridge University Press. ISBN 0-521-66097-1.
• Oostendorp, Cora (1987). The Bryophytes of the Palaeozoic and the Mesozoic. Bryophytorum Bibliotheca, Band 34. Berlin & Stuttgart: J. Cramer. ISBN 3-443-62006-X.
• Prihar, N. S. (1961). An Introduction to Embryophyta: Volume I, Bryophyta (4th ed.). Allahabad: Central Book Depot.
• 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.
• Schofield, W. B. (1985). Introduction to Bryology. New York: Macmillan. ISBN 0-02-949660-8.
• Watson, E. V. (1971). The Structure and Life of Bryophytes (3rd ed.). London: Hutchinson University Library. ISBN 0-09-109301-5.

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