Difference between revisions of "Marchantiophyta" - New World Encyclopedia

From New World Encyclopedia
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#REDIRECT [[Bryophyte]]
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{{Taxobox
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| fossil_range = {{fossil range|380}}Mid-[[Devonian]]<ref name="Hernick 2007" /> to recent
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| name = Liverworts
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| image = Haeckel Hepaticae.jpg
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| image_width = 240px
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| image_caption = "Hepaticae" from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904
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| regnum = [[Plant]]ae
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| divisio = '''Marchantiophyta'''
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| divisio_authority = Stotler & Stotl.-Crand., 1977<ref name="Stotlers 1977">{{cite journal | last = Stotler | first = Raymond E. | coauthors = Barbara J. Candall-Stotler | year = 1977 | title = A checklist of the liverworts and hornworts of North America | journal = The Bryologist | volume=80 | pages=405–428 | doi = 10.2307/3242017 }}</ref> emend. 2000<ref name="Stotlers 2000">Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". page 21 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1.</ref>
 +
| subdivision_ranks = Classes and Orders
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| subdivision =
 +
'''[[Haplomitriopsida]]''' <small>Stotler & Stotl.-Crand.</small>
 +
* [[Haplomitriales]] (Calobryales)
 +
* [[Treubiales]]
 +
'''Jungermanniopsida''' <small>Stotler & Stotl.-Crand.</small>
 +
* [[Metzgeriales]] (simple thalloids)
 +
* [[Jungermanniales]] (leafy liverworts)
 +
'''Marchantiopsida''' <small>Stotler & Stotl.-Crand.</small>
 +
* [[Blasiales]]
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* [[Sphaerocarpales]] (bottle liverworts)
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* [[Marchantiales]] (complex thalloids)
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}}
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 +
The '''Marchantiophyta''' {{Audio-IPA|en-us-Marchantiophyta.ogg|[mɑː(r)ˌkæntiˈɑːfɪtə]}} are a division of [[bryophyte]] [[plant]]s commonly referred to as '''hepatics''' or '''liverworts'''. Like other bryophytes, they have a [[gametophyte]]-dominant life cycle, in which cells of the plant carry only a single set of genetic information. 
 +
 
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It is estimated that there are 6000 to 8000 species of liverworts, though when [[Neotropical]] regions are better studied this number may approach 10,000.  Some of the more familiar species grow as a flattened leafless [[thallus (tissue)|thallus]], but most species are leafy with a form very much like a flattened [[moss]].  Leafy species can be distinguished from the apparently similar mosses on the basis of a number of features, including their single-celled [[rhizoid]]s. Leafy liverworts also differ from most (but not all) mosses in that their leaves never have a costa (present in many mosses) and may bear marginal cilia (very rare in mosses). Other differences are not universal for all mosses and liverworts, but the occurrence of leaves arranged in three ranks, the presence of deep lobes or segmented leaves, or a lack of clearly differentiated stem and leaves all point to the plant being a liverwort.
 +
 
 +
Liverworts are typically small, usually from 2-20 mm wide with individual plants less than 10 cm long, and are therefore often overlooked.  However, certain species may cover large patches of ground, rocks, trees or any other reasonably firm substrate on which they occur. They are distributed globally in almost every available habitat, most often in humid locations although there are desert and arctic species as well. Some species can be a nuisance in shady green-houses or a weed in gardens.<ref>Schuster, Rudolf M. ''The Hepaticae and Anthocerotae of North America'', volume VI, page 19. (Chicago: Field Museum of Natural History, 1992). ISBN 0-914-86821-7.</ref>
 +
 
 +
== Physical characteristics ==
 +
=== Description ===
 +
Most liverworts are small, usually from {{convert|2|-|20|mm|sigfig=1}} wide with individual plants less than {{convert|10|cm|sigfig=1}} long,<ref>Schuster, Rudolf M. ''The Hepaticae and Anthocerotae of North America'', volume I, pages 243-244. (New York: Columbia University Press, 1966)</ref> so they are often overlooked.  The most familiar liverworts consist of a prostrate, flattened, ribbon-like or branching structure called a [[Thallus (tissue)|thallus]] (plant body); these liverworts are termed ''thallose liverworts''.  However, most liverworts produce flattened stems with overlapping scales or leaves in three or more ranks, the middle rank being conspicuously different from the outer ranks; these are called ''[[Jungermanniales|leafy liverworts]]'' or ''scale liverworts''.<ref>Kashyap, Shiv Ram. ''Liverworts of the Western Himalayas and the Panjab Plain'', volume I, page 1. (New Delhi: The Chronica Botanica, 1929)</ref><ref name="Schofield 1985">Schofield, W. B. ''Introduction to Bryology'', pages 135-140. (New York: Macmillan, 1985). ISBN 0-02-949660-8.</ref> (''See the [[#Media|gallery]] below for examples.'')
 +
 
 +
[[Image:Lunularia cruciata.jpg|left|thumb|A [[Marchantiales|thallose liverwort]], ''Lunularia cruciata'']]
 +
Liverworts can most reliably be distinguished from the apparently similar [[moss]]es by their single-celled [[rhizoid]]s.<ref>Nehira, Kunito. "Spore Germination, Protonemata Development and Sporeling Development", page 347 ''in'' Rudolf M. Schuster (Ed.), ''New Manual of Bryology'', volume I. (Nichinan, Miyazaki, Japan: The Hattori Botanical Laboratory, 1983). ISBN 4-938163-3045.</ref>  Other differences are not universal for all mosses and all liverworts;<ref name="Schofield 1985" /> but the lack of clearly differentiated stem and leaves in thallose species, or in leafy species the presence of deeply lobed or segmented leaves and the presence of leaves arranged in three ranks, all point to the plant being a liverwort.<ref>Allison, K. W. & John Child. ''The Liverworts of New Zealand'', pages 13-14. (Dunedin: University of Otago Press, 1975).</ref><ref>Conard, Henry S. and Paul L. Redfearn, Jr. ''How to Know the Mosses and Liverworts'', revised ed., pages 12-23. (Dubuque, Iowa: William C. Brown Co., 1979) ISBN 0-697-04768-7</ref>  In addition, 90% of liverworts contain [[oil body|oil bodies]] in at least some of their cells, and these cellular structures are absent from most other bryophytes and from all vascular plants.<ref name="Bold 1987">Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. ''Morphology of Plants and Fungi'', 5th ed., page 189. (New York: Harper-Collins, 1987). ISBN 0-06-040838-1.</ref> The overall physical similarity of some mosses and leafy liverworts means that confirmation of the identification of some groups can be performed with certainty only with the aid of [[microscopy]] or an experienced bryologist.
 +
 
 +
Liverworts have a [[gametophyte]]-dominant life cycle, with the [[sporophyte]] dependent on the gametophyte.<ref name="Bold 1987" />  Cells in a typical liverwort plant each contain only a single set of genetic information, so the plant's cells are [[haploid]] for the majority of its life cycle. This contrasts sharply with the pattern exhibited by nearly all animals and by most other plants.  In the more familiar [[seed plant]]s, the haploid generation is represented only by the tiny [[pollen]] and the [[ovule]], while the [[diploid]] generation is the familiar tree or other plant.<ref>Fosket, Donald E. ''Plant Growth and Development: A Molecular Approach'', page 27. (San Diego: Academic Press, 1994). ISBN 0-12-262430-0.</ref>  Another unusual feature of the liverwort life cycle is that sporophytes (i.e. the [[diploid]] body) are very short-lived, withering away not long after releasing spores.<ref>Hicks, Marie L. ''Guide to the Liverworts of North Carolina'', page 10. (Durham: Duke University Press, 1992). ISBN 0-8223-1175-5.</ref> Even in other [[bryophyte]]s, the sporophyte is persistent and disperses spores over an extended period.
 +
 
 +
=== Life cycle ===
 +
[[Image:Liverwort life cycle.jpg|thumb|300px|Life cycle of a typical liverwort]]
 +
The life of a liverwort starts from the germination of a haploid [[spore]] to produce a [[protonema]], which is either a mass of thread-like filaments or else a flattened thallus.<ref>Nehira, Kunito. "Spore Germination, Protonemata Development and Sporeling Development", pages 358-374 ''in'' Rudolf M. Schuster (Ed.), ''New Manual of Bryology'', volume I. (Nichinan, Miyazaki, Japan: The Hattori Botanical Laboratory, 1983). ISBN 4-938163-3045.</ref><ref>Chopra, R. N. & P. K. Kumra. ''Biology of Bryophytes'', pages 1-38. (New York: John Wiley & Sons, 1988). ISBN 0-470-21359-0.</ref> The protonema is a transitory stage in the life of a liverwort, from which will grow the mature gametophore ("[[gamete]]-bearer") plant that produces the sex organs. The male organs are known as [[antheridium|antheridia]] (''singular:'' antheridium) and produce the sperm cells.  Clusters of antheridia are enclosed by a protective layer of cells called the '''perigonium''' (''plural:'' perigonia).  As in other land plants, the female organs are known as [[archegonium|archegonia]] (''singular:'' archegonium) and are protected by the thin surrounding '''perichaetum''' (''plural:'' perichaeta).<ref name="Schofield 1985" />  Each archegonium has a slender hollow tube, the "neck", down which the sperm swim to reach the egg cell.
 +
 
 +
Liverwort species may be either [[Bryophyte|dioicous]] or [[Bryophyte|monoicous]]. In dioicious liverworts, female and male sex organs are borne on different and separate gametophyte plants. In monoicious liverworts, the two kinds of reproductive structures are borne on different branches of the same plant.<ref>Malcolm, Bill & Nancy Malcolm. ''Mosses and Other Bryophytes: An Illustrated Glossary'', pages 6 & 128. (New Zealand: Micro-Optics Press, 2000). ISBN 0-473-06730-7.</ref> In either case, the sperm must swim from the antheridia where they are produced to the archegonium where the eggs are held.  The [[sperm]] of liverworts is ''biflagellate'', i.e. they have two tail-like [[flagellum|flagellae]] that aid in propulsion.<ref name="Campbell 1918">Campbell, Douglas H. ''The Structure and Development of Mosses and Ferns'', pages 73-74. (London: The Macmillan Co., 1918)</ref> Their journey is further assisted either by the splashing of raindrops or the presence of a thin layer of water covering the plants. Without water, the journey from antheridium to archegonium cannot occur.
 +
 
 +
In the presence of such water, sperm from the antheridia swim to the archegonia and [[fertilisation]] occurs, leading to the production of a diploid sporophyte. After fertilisation, the immature [[sporophyte]] within the archegonium develops three distinct regions: (1) a '''foot''', which both anchors the sporophyte in place and receives nutrients from its "mother" plant, (2) a spherical or ellipsoidal '''capsule''', inside which the spores will be produced for dispersing to new locations, and (3) a '''seta''' (stalk) which lies between the other two regions and connects them.<ref name="Campbell 1918" />  When the sporophyte has developed all three regions, the seta elongates, pushing its way out of the archegonium and rupturing it. While the foot remains anchored within the parent plant, the capsule is forced out by the seta and is extended away from the plant and into the air.  Within the capsule, cells divide to produce both [[elater]] cells and spore-producing cells.  The elaters are spring-like, and will push open the wall of the capsule to scatter themselves when the capsule bursts.  The spore-producing cells will undergo [[meiosis]] to form haploid [[spore]]s to disperse, upon which point the life cycle can start again.
 +
 
 +
== Ecology ==
 +
 
 +
Today, liverworts can be found in many ecosystems across the planet except the sea and excessively dry environments, or those exposed to high levels of direct solar radiation.<ref>Schuster, Rudolf M. ''The Hepaticae and Anthocerotae of North America'', volume I, pages 243-249. (New York: Columbia University Press, 1966).</ref> As with most groups of living plants, they are most common (both in numbers and species) in moist tropical areas.<ref>Pócs, Tamás. "Tropical Forest Bryophytes", page 59 ''in'' A. J. E. Smith (Ed.) ''Bryophyte Ecology''. (London: Chapman and Hall, 1982). ISBN 0-412-22340-6.</ref>  Liverworts are more commonly found in moderate to deep shade, though desert species may tolerate direct sunlight and periods of total desiccation.
 +
 
 +
== Classification ==
 +
=== Relationship to other plants ===
 +
Traditionally, the liverworts were grouped together with other [[bryophyte]]s ([[moss]]es and [[hornwort]]s) in the Division Bryophyta, within which the liverworts made up the class '''Hepaticae''' (also called Marchantiopsida).<ref>Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". page 36-38 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1</ref><ref name="Schofield 1985" />  However, since this grouping makes the Bryophyta [[paraphyletic]], the liverworts are now usually given their own division.<ref>Goffinet, Bernard. "Origin and phylogenetic relationships of bryophytes". pages 124-149 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1</ref> The use of the division name Bryophyta ''sensu latu'' is still found in the literature, but more frequently the [[Bryophyta]] now is used in a restricted sense to include only the mosses.
 +
 
 +
[[Image:Bryo cladogram.jpg|frame|center|Two hypotheses on the phylogeny of land plants (embryophyta).]]
 +
 
 +
Another reason that liverworts are now classified separately is that they appear to have diverged from all other [[embryophyte]] plants near the beginning of their [[evolution]]. The strongest line of supporting evidence is that liverworts are the only living group of land plants that do not have [[stoma]]ta on the [[sporophyte]] generation.<ref>Kenrick, Paul & Peter R. Crane. ''The Origin and Early Diversification of Land Plants: A Cladistic Study'', page 59. (Washington, D. C.: Smithsonian Institution Press, 1997). ISBN 1-56098-730-8.</ref>  Among the earliest [[fossil]]s believed to be liverworts are [[compression fossil]]s of ''[[Pallaviciniites]]'' from the Upper [[Devonian]] of [[New York]].<ref>Taylor, Thomas N. & Edith L. Taylor. ''The Biology and Evolution of Fossil Plants'', page 139. (Englewood Cliffs, NJ: Prentice Hall, 1993). ISBN 0-13-651589-4.</ref>  These fossils resemble modern species in the [[Metzgeriales]].<ref>Oostendorp, Cora. ''The Bryophytes of the Palaeozoic and the Mesozoic'', pages 70-71. (''Bryophytum Bibliotheca'', Band 34, 1987). ISBN 3-443-62006-X.</ref>  Another Devonian fossil called ''[[Protosalvinia]]'' also looks like a liverwort, but its relationship to other plants is still uncertain, so it may not belong to the Marchantiophyta. In 2007, the oldest fossils assignable to the liverworts were announced, ''Metzgeriothallus sharonae'' from the [[Givetian]] (Middle [[Devonian]]) of [[New York]], [[USA]].<ref name="Hernick 2007">{{cite journal
 +
| last = VanAller Hernick | first = L.
 +
| coauthors = Landing, E.; Bartowski, K.E.
 +
| year = 2008
 +
| title=Earth’s oldest liverworts—''Metzgeriothallus sharonae'' sp. nov. from the Middle Devonian (Givetian) of eastern New York, USA
 +
| doi = 10.1016/j.revpalbo.2007.09.002
 +
|volume=148
 +
|pages=154–162
 +
| journal = Review of Palaeobotany and Palynology }}</ref>
 +
 
 +
=== Internal classification ===
 +
[[Bryology|Bryologist]]s classify liverworts in the division '''Marchantiophyta'''. This divisional name is based on the name of the most universally recognized liverwort genus ''[[Marchantia]]''.<ref>Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". page 63 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1</ref>  In addition to this [[taxon]]-based name, the liverworts are often called '''Hepaticophyta'''. This name is derived from their common Latin name as Latin was the language in which botanists published their descriptions of species.  This name has led to some confusion, partly because it appears to be a taxon-based name derived from the [[genus]] ''[[Hepatica]]'' which is actually a [[flowering plant]] of the buttercup family [[Ranunculaceae]].  In addition, the name Hepaticophyta is frequently misspelled in textbooks as '''Hepatophyta''', which only adds to the confusion.
 +
 
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The Marchantiophyta is subdivided into three classes:<ref name="Forrest 2006">{{cite journal
 +
| last = Forrest | first = Laura L.
 +
| coauthors = Christine E. Davis, David G. Long, Barbara J. Crandall-Stotler, Alexandra Clark & Michelle L. Hollingsworth
 +
| year =  2006
 +
| title = Unraveling the evolutionary history of the liverworts (Marchantiophyta): multiple taxa, genomes and analyses
 +
| journal = The Bryologist | volume = 109 | issue = 3 | pages = 303–334
 +
| doi = 10.1639/0007-2745(2006)109[303:UTEHOT]2.0.CO;2 }}</ref><ref name="Heinrichs 2005">{{cite journal
 +
| last = Heinrichs | first = Jochen
 +
| coauthors = S. Robbert Gradstein, Rosemary Wilson, & Harald Schneider
 +
| year =  2005
 +
| title = Towards a natural classification of liverworts (Marchantiophyta) based on the chloroplast gene rbcL
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| journal = Cryptogamie Bryologie | volume = 26 | issue = 2 | pages = 131–150 }}</ref><ref name="He-Nygrén 2006">{{cite journal
 +
| last = He-Nygrén | first = Xiaolan
 +
| coauthors = Aino Juslén, Inkeri Ahonen, David Glenny, & Sinikka Piippo
 +
| year =  2006
 +
| title = Illuminating the evolutionary history of liverworts (Marchantiophyta)—towards a natural classification
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| journal = Cladistics | volume = 22 | issue = 1 | pages = 1–31
 +
| doi = 10.1111/j.1096-0031.2006.00089.x }}</ref><ref name="Renzaglia 2007">{{cite journal
 +
| last = Renzaglia | first = Karen S.
 +
| coauthors = Scott Schuette, R. Joel Duff, Roberto Ligrone, A. Jonathan Shaw, Brent D. Mishler, & Jeffrey G. Duckett
 +
| year =  2007
 +
| title = Bryophyte phylogeny: Advancing the molecular and morphological frontiers
 +
| journal = The Bryologist | volume = 110 | issue = 2 | pages = 179–213
 +
| doi = 10.1639/0007-2745(2007)110[179:BPATMA]2.0.CO;2 }}</ref>
 +
 
 +
* The '''Jungermanniopsida''' includes the two [[order (biology)|orders]] [[Metzgeriales]] (simple thalloids) and [[Jungermanniales]] (leafy liverworts). 
 +
* The '''Marchantiopsida''' includes the three orders [[Marchantiales]] (complex-thallus liverworts), and [[Sphaerocarpales]] (bottle hepatics), as well as the [[Blasiales]] (previously placed among the Metzgeriales).<ref name="Forrest 2006" />  It also includes the problematic genus ''[[Monoclea]]'', which is sometimes placed in its own order Monocleales.<ref>Schuster, Rudolf M. ''The Hepaticae and Anthocerotae of North America'', volume VI, page 26. (Chicago: Field Museum of Natural History, 1992). ISBN 0-914-86821-7.</ref> 
 +
* A third class, the '''[[Haplomitriopsida]]''' is newly recognized as a basal sister group to the other liverworts;<ref name="Renzaglia 2007" /> it comprises the genera ''[[Haplomitrium]]'', ''[[Treubia]]'', and ''[[Apotreubia]]''.
 +
 
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It is estimated that there are 6000 to 8000 species of liverworts, at least 85% of which belong to the leafy group.<ref name="Stotlers 2000" />
 +
 
 +
== Economic importance ==
 +
 
 +
In ancient times, it was believed that liverworts cured diseases of the [[liver]], hence the name.<ref>Dittmer, Howard J. ''Phylogeny and Form in the Plant Kingdom'', page 286. (Toronto: D. Van Nostrand Co., 1964)</ref> In [[Old English]], the word liverwort literally means ''liver plant''.<ref>Raven, P. H., R. F. Evert, & S. E. Eichhorn. ''Biology of Plants'', 7th ed., page 351. (New York: W. H. Freeman, 2005). ISBN 0-7167-1007-2.</ref> This probably stemmed from the superficial appearance of some thalloid liverworts (which resemble a liver in outline), and led to the common name of the group as ''hepatics'', from the [[Latin]] word ''hēpaticus'' for "belonging to the liver". An unrelated flowering plant, ''[[Hepatica]]'', is sometimes also referred to as liverwort because it was once also used in treating diseases of the liver. This archaic relationship of plant form to function was based in the [[Doctrine of signatures|"Doctrine of Signatures"]].<ref>Stern, Kingsley R. ''Introductory Plant Biology'', 5th ed., page 338. (Dubuque, Iowa: Wm. C. Brown Publishers, 1991) ISBN 0-697-09947-4.</ref>
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 +
Liverworts have little direct economic importance today.  Their greatest impact is indirect, though the reduction of erosion along streambanks, their collection and retention of water in tropical forests, and the formation of [[soil crust]]s in deserts and polar regions.  However, a few species are used by humans directly.  A few species, such as ''[[Riccia fluitans]]'', are aquatic thallose liverworts sold for use in [[Aquarium|aquaria]].  Their thin, slender branches float on the water's surface and provide habitat for both small invertebrates and the fish that feed on them.
 +
 
 +
== Gallery ==
 +
<!-- Please do not add images to this gallery simply because the image exists.  The collection of images below was selected to (1) illustrate the overall structural diversity of the two major groups of liverworts, and (2) to show key structures described within the article.  Additional images are better placed among the article text or uploaded to Commons. —>
 +
A small collection of images showing liverwort structure and diversity:
 +
<gallery>
 +
Image:Marchantia.jpg|<center>''[[Marchantia]] polymorpha'', with antheridial and archegonial stalks.</center>
 +
Image:Archegonium.jpg|<center>The [[archegonium]] of ''Porella''.</center>
 +
Image:Porella SPT.jpg|<center>A sporophyte emerging from its archegonium.</center>
 +
Image:Porella platyphylla.jpg|<center>''[[Porella]] platyphylla'' clump growing on a tree.</center>
 +
Image:Pellia epiphylla5 ies.jpg|<center>''[[Pellia]] epiphylla'', growing on moist soil.</center>
 +
Image:Plagiochila aspleniodes0.jpg|<center>''[[Plagiochila]] asplenioides'', a [[Jungermanniales|leafy liverwort]].</center>
 +
Image:RicciaFluitans1.jpg|<center>''[[Riccia fluitans]]'', an aquatic [[Marchantiales|thallose liverwort]].</center>
 +
Image:Liverwort.jpg|<center>''[[Conocephalum]] conicum'', a large thallose liverwort.</center>
 +
</gallery>
 +
 
 +
== See also ==
 +
* [[Bryophyte]]
 +
* [[Embryophyte]]
 +
 
 +
== References ==
 +
{{Reflist|2}}
 +
 
 +
== External links ==
 +
{{Commonscat|Marchantiophyta}}
 +
{{Wikispecies|Marchantiophyta}}
 +
{{wiktionary|liverwort}}
 +
* [http://www.pflanzenliebe.de/innen/innen_moose/innen_moose.html Picture Gallery of Mosses & Liverworts]
 +
* [http://www2.una.edu/pdavis/hepatic_orders.htm  Liverwort structure in pictures]
 +
* [http://bryophytes.plant.siu.edu/marchantiophyta.html  Liverwort classification scheme]
 +
* [http://www.biology.duke.edu/bryology/LiToL/ LiToL: Assembling the Liverwort Tree of Life] (note: for 500,000 million years ago read "480 million years ago".)
 +
* [http://www.bio.ilstu.edu/armstrong/syllabi/222book/chapt6.htm  Inter-relationships of Mosses, Liverworts, and Hornworts]
 +
* [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Mosses.html  Moss-Liverwort connection]
 +
* [http://www.bio.umass.edu/biology/conn.river/liverwts.html  Additional information on Liverworts]
 +
* [http://www.hcs.ohio-state.edu/hcs300/liver1.htm  Liverworts]
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[[Category:Life sciences]]
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[[Category:Plants]]
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 +
{{credit|Marchantiophyta|244926418}}

Revision as of 16:43, 20 October 2008

Liverworts
Fossil range: 380 Ma
↓
Mid-Devonian[1] to recent
"Hepaticae" from Ernst Haeckel's Kunstformen der Natur, 1904
"Hepaticae" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification
Kingdom: Plantae
Division: Marchantiophyta
Stotler & Stotl.-Crand., 1977[2] emend. 2000[3]
Classes and Orders

Haplomitriopsida Stotler & Stotl.-Crand.

  • Haplomitriales (Calobryales)
  • Treubiales

Jungermanniopsida Stotler & Stotl.-Crand.

  • Metzgeriales (simple thalloids)
  • Jungermanniales (leafy liverworts)

Marchantiopsida Stotler & Stotl.-Crand.

  • Blasiales
  • Sphaerocarpales (bottle liverworts)
  • Marchantiales (complex thalloids)

The Marchantiophyta [mɑː(r)ˌkæntiˈɑːfɪtə] (help·info) are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information.

It is estimated that there are 6000 to 8000 species of liverworts, though when Neotropical regions are better studied this number may approach 10,000. Some of the more familiar species grow as a flattened leafless thallus, but most species are leafy with a form very much like a flattened moss. Leafy species can be distinguished from the apparently similar mosses on the basis of a number of features, including their single-celled rhizoids. Leafy liverworts also differ from most (but not all) mosses in that their leaves never have a costa (present in many mosses) and may bear marginal cilia (very rare in mosses). Other differences are not universal for all mosses and liverworts, but the occurrence of leaves arranged in three ranks, the presence of deep lobes or segmented leaves, or a lack of clearly differentiated stem and leaves all point to the plant being a liverwort.

Liverworts are typically small, usually from 2-20 mm wide with individual plants less than 10 cm long, and are therefore often overlooked. However, certain species may cover large patches of ground, rocks, trees or any other reasonably firm substrate on which they occur. They are distributed globally in almost every available habitat, most often in humid locations although there are desert and arctic species as well. Some species can be a nuisance in shady green-houses or a weed in gardens.[4]

Physical characteristics

Description

Most liverworts are small, usually from 2–20 millimeters (Template:Convert/Dual/srnd) wide with individual plants less than 10 centimeters (4 in) long,[5] so they are often overlooked. The most familiar liverworts consist of a prostrate, flattened, ribbon-like or branching structure called a thallus (plant body); these liverworts are termed thallose liverworts. However, most liverworts produce flattened stems with overlapping scales or leaves in three or more ranks, the middle rank being conspicuously different from the outer ranks; these are called leafy liverworts or scale liverworts.[6][7] (See the gallery below for examples.)

A thallose liverwort, Lunularia cruciata

Liverworts can most reliably be distinguished from the apparently similar mosses by their single-celled rhizoids.[8] Other differences are not universal for all mosses and all liverworts;[7] but the lack of clearly differentiated stem and leaves in thallose species, or in leafy species the presence of deeply lobed or segmented leaves and the presence of leaves arranged in three ranks, all point to the plant being a liverwort.[9][10] In addition, 90% of liverworts contain oil bodies in at least some of their cells, and these cellular structures are absent from most other bryophytes and from all vascular plants.[11] The overall physical similarity of some mosses and leafy liverworts means that confirmation of the identification of some groups can be performed with certainty only with the aid of microscopy or an experienced bryologist.

Liverworts have a gametophyte-dominant life cycle, with the sporophyte dependent on the gametophyte.[11] Cells in a typical liverwort plant each contain only a single set of genetic information, so the plant's cells are haploid for the majority of its life cycle. This contrasts sharply with the pattern exhibited by nearly all animals and by most other plants. In the more familiar seed plants, the haploid generation is represented only by the tiny pollen and the ovule, while the diploid generation is the familiar tree or other plant.[12] Another unusual feature of the liverwort life cycle is that sporophytes (i.e. the diploid body) are very short-lived, withering away not long after releasing spores.[13] Even in other bryophytes, the sporophyte is persistent and disperses spores over an extended period.

Life cycle

Life cycle of a typical liverwort

The life of a liverwort starts from the germination of a haploid spore to produce a protonema, which is either a mass of thread-like filaments or else a flattened thallus.[14][15] The protonema is a transitory stage in the life of a liverwort, from which will grow the mature gametophore ("gamete-bearer") plant that produces the sex organs. The male organs are known as antheridia (singular: antheridium) and produce the sperm cells. Clusters of antheridia are enclosed by a protective layer of cells called the perigonium (plural: perigonia). As in other land plants, the female organs are known as archegonia (singular: archegonium) and are protected by the thin surrounding perichaetum (plural: perichaeta).[7] Each archegonium has a slender hollow tube, the "neck", down which the sperm swim to reach the egg cell.

Liverwort species may be either dioicous or monoicous. In dioicious liverworts, female and male sex organs are borne on different and separate gametophyte plants. In monoicious liverworts, the two kinds of reproductive structures are borne on different branches of the same plant.[16] In either case, the sperm must swim from the antheridia where they are produced to the archegonium where the eggs are held. The sperm of liverworts is biflagellate, i.e. they have two tail-like flagellae that aid in propulsion.[17] Their journey is further assisted either by the splashing of raindrops or the presence of a thin layer of water covering the plants. Without water, the journey from antheridium to archegonium cannot occur.

In the presence of such water, sperm from the antheridia swim to the archegonia and fertilisation occurs, leading to the production of a diploid sporophyte. After fertilisation, the immature sporophyte within the archegonium develops three distinct regions: (1) a foot, which both anchors the sporophyte in place and receives nutrients from its "mother" plant, (2) a spherical or ellipsoidal capsule, inside which the spores will be produced for dispersing to new locations, and (3) a seta (stalk) which lies between the other two regions and connects them.[17] When the sporophyte has developed all three regions, the seta elongates, pushing its way out of the archegonium and rupturing it. While the foot remains anchored within the parent plant, the capsule is forced out by the seta and is extended away from the plant and into the air. Within the capsule, cells divide to produce both elater cells and spore-producing cells. The elaters are spring-like, and will push open the wall of the capsule to scatter themselves when the capsule bursts. The spore-producing cells will undergo meiosis to form haploid spores to disperse, upon which point the life cycle can start again.

Ecology

Today, liverworts can be found in many ecosystems across the planet except the sea and excessively dry environments, or those exposed to high levels of direct solar radiation.[18] As with most groups of living plants, they are most common (both in numbers and species) in moist tropical areas.[19] Liverworts are more commonly found in moderate to deep shade, though desert species may tolerate direct sunlight and periods of total desiccation.

Classification

Relationship to other plants

Traditionally, the liverworts were grouped together with other bryophytes (mosses and hornworts) in the Division Bryophyta, within which the liverworts made up the class Hepaticae (also called Marchantiopsida).[20][7] However, since this grouping makes the Bryophyta paraphyletic, the liverworts are now usually given their own division.[21] The use of the division name Bryophyta sensu latu is still found in the literature, but more frequently the Bryophyta now is used in a restricted sense to include only the mosses.

Two hypotheses on the phylogeny of land plants (embryophyta).

Another reason that liverworts are now classified separately is that they appear to have diverged from all other embryophyte plants near the beginning of their evolution. The strongest line of supporting evidence is that liverworts are the only living group of land plants that do not have stomata on the sporophyte generation.[22] Among the earliest fossils believed to be liverworts are compression fossils of Pallaviciniites from the Upper Devonian of New York.[23] These fossils resemble modern species in the Metzgeriales.[24] Another Devonian fossil called Protosalvinia also looks like a liverwort, but its relationship to other plants is still uncertain, so it may not belong to the Marchantiophyta. In 2007, the oldest fossils assignable to the liverworts were announced, Metzgeriothallus sharonae from the Givetian (Middle Devonian) of New York, USA.[1]

Internal classification

Bryologists classify liverworts in the division Marchantiophyta. This divisional name is based on the name of the most universally recognized liverwort genus Marchantia.[25] In addition to this taxon-based name, the liverworts are often called Hepaticophyta. This name is derived from their common Latin name as Latin was the language in which botanists published their descriptions of species. This name has led to some confusion, partly because it appears to be a taxon-based name derived from the genus Hepatica which is actually a flowering plant of the buttercup family Ranunculaceae. In addition, the name Hepaticophyta is frequently misspelled in textbooks as Hepatophyta, which only adds to the confusion.

The Marchantiophyta is subdivided into three classes:[26][27][28][29]

  • The Jungermanniopsida includes the two orders Metzgeriales (simple thalloids) and Jungermanniales (leafy liverworts).
  • The Marchantiopsida includes the three orders Marchantiales (complex-thallus liverworts), and Sphaerocarpales (bottle hepatics), as well as the Blasiales (previously placed among the Metzgeriales).[26] It also includes the problematic genus Monoclea, which is sometimes placed in its own order Monocleales.[30]
  • A third class, the Haplomitriopsida is newly recognized as a basal sister group to the other liverworts;[29] it comprises the genera Haplomitrium, Treubia, and Apotreubia.

It is estimated that there are 6000 to 8000 species of liverworts, at least 85% of which belong to the leafy group.[3]

Economic importance

In ancient times, it was believed that liverworts cured diseases of the liver, hence the name.[31] In Old English, the word liverwort literally means liver plant.[32] This probably stemmed from the superficial appearance of some thalloid liverworts (which resemble a liver in outline), and led to the common name of the group as hepatics, from the Latin word hēpaticus for "belonging to the liver". An unrelated flowering plant, Hepatica, is sometimes also referred to as liverwort because it was once also used in treating diseases of the liver. This archaic relationship of plant form to function was based in the "Doctrine of Signatures".[33]

Liverworts have little direct economic importance today. Their greatest impact is indirect, though the reduction of erosion along streambanks, their collection and retention of water in tropical forests, and the formation of soil crusts in deserts and polar regions. However, a few species are used by humans directly. A few species, such as Riccia fluitans, are aquatic thallose liverworts sold for use in aquaria. Their thin, slender branches float on the water's surface and provide habitat for both small invertebrates and the fish that feed on them.

Gallery

A small collection of images showing liverwort structure and diversity:

  • Marchantia polymorpha, with antheridial and archegonial stalks.
  • The archegonium of Porella.
  • A sporophyte emerging from its archegonium.
  • Porella platyphylla clump growing on a tree.
  • Pellia epiphylla, growing on moist soil.
  • Plagiochila asplenioides, a leafy liverwort.
  • Riccia fluitans, an aquatic thallose liverwort.
  • Conocephalum conicum, a large thallose liverwort.

See also

References
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  1. ↑ 1.0 1.1 VanAller Hernick, L. and Landing, E.; Bartowski, K.E. (2008). Earth’s oldest liverworts—Metzgeriothallus sharonae sp. nov. from the Middle Devonian (Givetian) of eastern New York, USA. Review of Palaeobotany and Palynology 148: 154–162.
  2. ↑ Stotler, Raymond E. and Barbara J. Candall-Stotler (1977). A checklist of the liverworts and hornworts of North America. The Bryologist 80: 405–428.
  3. ↑ 3.0 3.1 Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". page 21 in A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1.
  4. ↑ Schuster, Rudolf M. The Hepaticae and Anthocerotae of North America, volume VI, page 19. (Chicago: Field Museum of Natural History, 1992). ISBN 0-914-86821-7.
  5. ↑ Schuster, Rudolf M. The Hepaticae and Anthocerotae of North America, volume I, pages 243-244. (New York: Columbia University Press, 1966)
  6. ↑ Kashyap, Shiv Ram. Liverworts of the Western Himalayas and the Panjab Plain, volume I, page 1. (New Delhi: The Chronica Botanica, 1929)
  7. ↑ 7.0 7.1 7.2 7.3 Schofield, W. B. Introduction to Bryology, pages 135-140. (New York: Macmillan, 1985). ISBN 0-02-949660-8.
  8. ↑ Nehira, Kunito. "Spore Germination, Protonemata Development and Sporeling Development", page 347 in Rudolf M. Schuster (Ed.), New Manual of Bryology, volume I. (Nichinan, Miyazaki, Japan: The Hattori Botanical Laboratory, 1983). ISBN 4-938163-3045.
  9. ↑ Allison, K. W. & John Child. The Liverworts of New Zealand, pages 13-14. (Dunedin: University of Otago Press, 1975).
  10. ↑ Conard, Henry S. and Paul L. Redfearn, Jr. How to Know the Mosses and Liverworts, revised ed., pages 12-23. (Dubuque, Iowa: William C. Brown Co., 1979) ISBN 0-697-04768-7
  11. ↑ 11.0 11.1 Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. Morphology of Plants and Fungi, 5th ed., page 189. (New York: Harper-Collins, 1987). ISBN 0-06-040838-1.
  12. ↑ Fosket, Donald E. Plant Growth and Development: A Molecular Approach, page 27. (San Diego: Academic Press, 1994). ISBN 0-12-262430-0.
  13. ↑ Hicks, Marie L. Guide to the Liverworts of North Carolina, page 10. (Durham: Duke University Press, 1992). ISBN 0-8223-1175-5.
  14. ↑ Nehira, Kunito. "Spore Germination, Protonemata Development and Sporeling Development", pages 358-374 in Rudolf M. Schuster (Ed.), New Manual of Bryology, volume I. (Nichinan, Miyazaki, Japan: The Hattori Botanical Laboratory, 1983). ISBN 4-938163-3045.
  15. ↑ Chopra, R. N. & P. K. Kumra. Biology of Bryophytes, pages 1-38. (New York: John Wiley & Sons, 1988). ISBN 0-470-21359-0.
  16. ↑ Malcolm, Bill & Nancy Malcolm. Mosses and Other Bryophytes: An Illustrated Glossary, pages 6 & 128. (New Zealand: Micro-Optics Press, 2000). ISBN 0-473-06730-7.
  17. ↑ 17.0 17.1 Campbell, Douglas H. The Structure and Development of Mosses and Ferns, pages 73-74. (London: The Macmillan Co., 1918)
  18. ↑ Schuster, Rudolf M. The Hepaticae and Anthocerotae of North America, volume I, pages 243-249. (New York: Columbia University Press, 1966).
  19. ↑ Pócs, Tamás. "Tropical Forest Bryophytes", page 59 in A. J. E. Smith (Ed.) Bryophyte Ecology. (London: Chapman and Hall, 1982). ISBN 0-412-22340-6.
  20. ↑ Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". page 36-38 in A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1
  21. ↑ Goffinet, Bernard. "Origin and phylogenetic relationships of bryophytes". pages 124-149 in A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1
  22. ↑ Kenrick, Paul & Peter R. Crane. The Origin and Early Diversification of Land Plants: A Cladistic Study, page 59. (Washington, D. C.: Smithsonian Institution Press, 1997). ISBN 1-56098-730-8.
  23. ↑ Taylor, Thomas N. & Edith L. Taylor. The Biology and Evolution of Fossil Plants, page 139. (Englewood Cliffs, NJ: Prentice Hall, 1993). ISBN 0-13-651589-4.
  24. ↑ Oostendorp, Cora. The Bryophytes of the Palaeozoic and the Mesozoic, pages 70-71. (Bryophytum Bibliotheca, Band 34, 1987). ISBN 3-443-62006-X.
  25. ↑ Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". page 63 in A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology. (Cambridge: Cambridge University Press:2000). ISBN 0-521-66097-1
  26. ↑ 26.0 26.1 Forrest, Laura L. and Christine E. Davis, David G. Long, Barbara J. Crandall-Stotler, Alexandra Clark & Michelle L. Hollingsworth (2006). Unraveling the evolutionary history of the liverworts (Marchantiophyta): multiple taxa, genomes and analyses. The Bryologist 109 (3): 303–334.
  27. ↑ Heinrichs, Jochen and S. Robbert Gradstein, Rosemary Wilson, & Harald Schneider (2005). Towards a natural classification of liverworts (Marchantiophyta) based on the chloroplast gene rbcL. Cryptogamie Bryologie 26 (2): 131–150.
  28. ↑ He-Nygrén, Xiaolan and Aino Juslén, Inkeri Ahonen, David Glenny, & Sinikka Piippo (2006). Illuminating the evolutionary history of liverworts (Marchantiophyta)—towards a natural classification. Cladistics 22 (1): 1–31.
  29. ↑ 29.0 29.1 Renzaglia, Karen S. and Scott Schuette, R. Joel Duff, Roberto Ligrone, A. Jonathan Shaw, Brent D. Mishler, & Jeffrey G. Duckett (2007). Bryophyte phylogeny: Advancing the molecular and morphological frontiers. The Bryologist 110 (2): 179–213.
  30. ↑ Schuster, Rudolf M. The Hepaticae and Anthocerotae of North America, volume VI, page 26. (Chicago: Field Museum of Natural History, 1992). ISBN 0-914-86821-7.
  31. ↑ Dittmer, Howard J. Phylogeny and Form in the Plant Kingdom, page 286. (Toronto: D. Van Nostrand Co., 1964)
  32. ↑ Raven, P. H., R. F. Evert, & S. E. Eichhorn. Biology of Plants, 7th ed., page 351. (New York: W. H. Freeman, 2005). ISBN 0-7167-1007-2.
  33. ↑ Stern, Kingsley R. Introductory Plant Biology, 5th ed., page 338. (Dubuque, Iowa: Wm. C. Brown Publishers, 1991) ISBN 0-697-09947-4.

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