View source for Liverwort

{{Short description|Division of non-vascular land plants}}
{{For|the genus of flowering plants|Hepatica}}
{{Use dmy dates|date=July 2022}}
{{Automatic taxobox
| name = Liverworts
| fossil_range = {{fossil range|472|0}}Mid-[[Ordovician]]<ref name="Walker-2010" /> to [[Holocene|present]]
| image = A mikxture of liverworts from Kunstformen der Natur (1904), plate 82.jpg
| image_caption = "Hepaticae" from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904
| display_parents = 2
| taxon = Marchantiophyta
| authority = Stotler & Stotl.-Crand., 1977<ref name="Stotler-1977">{{cite journal | last = Stotler | first = Raymond E. |author2=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 | jstor = 3242017 | issue = 3 | publisher = American Bryological and Lichenological Society }}</ref> emend. 2000<ref name="Crandall-Stotler-2000">{{cite book | last1=Crandall-Stotler | first1=Barbara | last2=Stotler | first2=Raymond E. | year=2000 | chapter=Morphology and classification of the Marchantiophyta | page=21 |editor=A. Jonathan Shaw |editor2=Bernard Goffinet | title=Bryophyte Biology | location=Cambridge | publisher=Cambridge University Press | isbn=0-521-66097-1 }}</ref>
| type_genus = ''[[Marchantia]]'' <small> [[Carl Linnaeus|L.]], 1753</small>
| subdivision_ranks = Classes and orders
| subdivision = * [[Haplomitriopsida]]
** [[Calobryales]]
** [[Treubiales]]
* [[Marchantiopsida]]
** [[Blasiales]]
** [[Lunulariales]]
** [[Marchantiales]] 
** [[Neohodgsoniales]]
** [[Sphaerocarpales]] 
* [[Jungermanniopsida]] 
** [[Fossombroniales]] 
** [[Jungermanniales]] 
** [[Metzgeriales]]
** [[Pallaviciniales]]
** [[Pelliales]]  
** [[Pleuroziales]]
** [[Porellales]] 
** [[Ptilidiales]]
| synonyms = * Hepaticae <small>[[Antoine Laurent de Jussieu|Juss.]], 1789</small>
* Marchantiophytina <small>[[Alexander Borissovitch Doweld|Doweld]], 2001</small>
* Hepaticophyta <small>Crand.-Stotl et Stotler, 2000</small>
* Hepatophyta <small>Stotler et Crand.-Stotl, 1977</small>
* Jungermanniophyta
}}
'''Liverworts''' are a group of [[non-vascular plant|non-vascular]] [[embryophyte|land plant]]s forming the division '''Marchantiophyta''' ({{IPAc-en|m|ɑr|ˌ|k|æ|n|t|i|ˈ|ɒ|f|ə|t|ə|,_|-|oʊ|ˈ|f|aɪ|t|ə|audio=en-us-Marchantiophyta.ogg}}). They may also be referred to as  '''hepatics'''. Like [[mosses]] and [[hornworts]], they have a [[gametophyte]]-dominant life cycle, in which cells of the plant carry only a single set of genetic information. The division name was derived from the genus name ''[[Marchantia]]'', named  after his father by French botanist [[Jean Marchant]].

It is estimated that there are about 9000 species of liverwort.<ref>{{Cite web |url=https://www.unb.ca/research/liverworts/ |title=Liverworts Homepage {{!}} UNB |access-date=10 June 2020 |archive-date=24 July 2021 |archive-url=https://web.archive.org/web/20210724103956/https://www.unb.ca/research/liverworts/ |url-status=dead }}</ref> 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 [[rhizoid]]s. Leafy liverworts also differ from most (but not all) mosses in that their leaves never have a [[costa (botany)|costa]] (present in many mosses) and may bear marginal [[cilia (botany)|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 distinguished from mosses in having unique [[complex oil bodies]] of high refractive index.

Liverworts are typically small, usually from {{cvt|2|to|20|mm}} wide with individual plants less than {{cvt|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 greenhouses or a weed in gardens.<ref>{{cite book |last=Schuster |first=Rudolf M. |title=The Hepaticae and Anthocerotae of North America |volume=VI |page=19 |location=Chicago |publisher=Field Museum of Natural History |date=1992 |isbn=0-914868-21-7}}</ref>

== Physical characteristics ==

=== Description ===

Most liverworts are small, measuring from {{convert|2|to|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'', vol. I, pp. 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]] (plant body); these liverworts are termed ''thallose liverworts''. However, most liverworts produce flattened stems with overlapping scales or leaves in two or more ranks, the middle rank is often 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'', vol. I, p. 1. (New Delhi: The Chronica Botanica, 1929)</ref><ref name="Schofield">Schofield, W. B. ''Introduction to Bryology'', pp. 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", p. 347 ''in'' Rudolf M. Schuster (Ed.), ''New Manual of Bryology'', volume I. (Nichinan, Miyazaki, Japan: The Hattori Botanical Laboratory, 1983). {{Listed Invalid ISBN|49381633045}}.</ref> Other differences are not universal for all mosses and all liverworts;<ref name="Schofield" /> 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,<ref>Allison, K. W. & John Child. ''The Liverworts of New Zealand'', pp. 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., pp. 12–23. (Dubuque, Iowa: William C. Brown Co., 1979) {{ISBN|0-697-04768-7}}</ref> as well as frequent dichotomous branching, all point to the plant being a liverwort. With a few exceptions, all liverworts undergo polyplastidic meiosis, in contrast to mosses and hornworts which have monoplastidic meiosis.<ref>{{cite journal | last1=Renzaglia | first1=K. S. | last2=Ashton | first2=N. W. | last3=Suh | first3=D. Y. | title=Sporogenesis in Physcomitrium patens: Intergenerational collaboration and the development of the spore wall and aperture | journal=Frontiers in Cell and Developmental Biology | date=2023 | volume=11 | article-number=1165293 | doi=10.3389/fcell.2023.1165293 | doi-access=free | pmid=37123413 | pmc=10133578 }}</ref> Unlike any other embryophytes, most liverworts contain [[Complex oil bodies|unique membrane-bound oil bodies]] containing isoprenoids in at least some of their cells, lipid droplets in the cytoplasm of all other plants being unenclosed.<ref name="Harold-1987">Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. ''Morphology of Plants and Fungi'', 5th ed., p. 189. (New York: Harper-Collins, 1987). {{ISBN|0-06-040839-1}}.</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, like other bryophytes, have a [[gametophyte]]-dominant life cycle, with the [[sporophyte]] dependent on the gametophyte.<ref name="Harold-1987" /> The sporophyte of many liverworts are non-photosynthetic, but there are also several that are photosynthetic to various degrees.<ref>[https://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1063&context=bryo-ecol-subchapters Volume 1, Chapter 11-1: Photosynthesis: The Process]</ref> 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 vascular 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'', p. 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'', p. 10. (Durham: Duke University Press, 1992). {{ISBN|0-8223-1175-5}}.</ref> In mosses, the sporophyte is more persistent and in hornworts, the sporophyte disperses spores over an extended period.<ref>{{cite book |last1=Simpson |first1=Michael G. |title=Plant Systematics |chapter=Evolution and Diversity of Green and Land Plants |date=2019 |pages=55–74 |doi=10.1016/b978-0-12-812628-8.50003-1 |isbn=978-0-12-812628-8 }}</ref>

=== Life cycle ===<!-- This section is linked from "Alternation of generations"; be sure to change the link there if you change the title of this section. -->

[[Image:Liverwort life cycle.jpg|thumb|300px|Sexual life cycle of a ''Marchantia''-like 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 a flattened thallus.<ref>Nehira, Kunito. "Spore Germination, Protonemata Development and Sporeling Development", pp. 358–374 ''in'' Rudolf M. Schuster (Ed.), ''New Manual of Bryology'', volume I. (Nichinan, Miyazaki, Japan: The Hattori Botanical Laboratory, 1983). {{Listed Invalid ISBN|49381633045}}.</ref><ref>Chopra, R. N. & P. K. Kumra. ''Biology of Bryophytes'', pp. 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" /> 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 dioicous liverworts, female and male sex organs are borne on different and separate gametophyte plants. In monoicous 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'', pp. 6 & 128. (New Zealand: Micro-Optics Press, 2000). {{ISBN|0-473-06730-7}}.</ref> In either case, the sperm must move 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 enable them to swim short distances,<ref name="Campbell-1918">[https://www.biodiversitylibrary.org/item/25364#7 Campbell, Douglas H. ''The Structure and Development of Mosses and Ferns'', pp. 73–74. (London: The Macmillan Co., 1918)]</ref> provided that at least a thin film of water is present. Their journey may be assisted by the splashing of raindrops. In 2008, Japanese researchers discovered that some liverworts are able to fire sperm-containing water up to 15&nbsp;cm in the air, enabling them to fertilize female plants growing more than a metre from the nearest male.<ref>{{Cite journal |last=Pain |first=S. |year=2010 |title=Botanical ballistics |journal=New Scientist |volume=208 |issue=2792/3 |pages=45–47 |doi=10.1016/s0262-4079(10)63177-6}}</ref>

When sperm reach the archegonia, [[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" /> The sporophyte lacks an [[apical meristem]], an [[auxin]]-sensitive point of divergence with other land plants some time in the [[Late Silurian]]/[[Early Devonian]].<ref name="Cooke-2003">{{cite book |last1=Cooke |first1=Todd J. |last2=Poli |first2=Dorothybelle |last3=Cohen |first3=Jerry D. |title=The Evolution of Plant Physiology |chapter=Did auxin play a crucial role in the evolution of novel body plans during the Late Silurian-Early Devonian radiation of land plants? |date=2004 |pages=85–107 |doi=10.1016/b978-012339552-8/50006-8 |isbn=978-0-12-339552-8 }}</ref><ref name="Friedman-2004">{{cite journal |last1=Friedman |first1=William E. |last2=Moore |first2=Richard C. |last3=Purugganan |first3=Michael D. |title=The evolution of plant development |journal=American Journal of Botany |date=2004 |volume=91 |issue=10 |pages=1726–1741 |doi=10.3732/ajb.91.10.1726 |pmid=21652320 |bibcode=2004AmJB...91.1726F }}</ref> 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.

==== Asexual reproduction ====

Some liverworts are capable of [[asexual reproduction]]; in bryophytes in general "it would almost be true to say that vegetative reproduction is the rule and not the exception."<ref name="Lepp-Apr 2008b">{{cite web | url=http://www.anbg.gov.au/bryophyte/vegetative-reproduction.html | title=Vegetative Reproduction | publisher=Australian National Botanic Gardens | work=Australian Bryophytes | date=15 April 2008 | access-date=December 22, 2011 | author=Lepp, Heino}}</ref> For example, in ''[[Riccia]]'', when the older parts of the forked thalli die, the younger tips become separate individuals.<ref name="Lepp-Apr 2008b"/>

Some thallose liverworts such as ''[[Marchantia polymorpha]]'' and ''[[Lunularia|Lunularia cruciata]]'' produce small disc-shaped [[Gemma (botany)|gemmae]] in shallow cups.<ref>Smith, AJE (1989) ''The Liverworts of Britain and Ireland'', Cambridge University Press, Cambridge.</ref> ''Marchantia'' gemmae can be dispersed up to 120&nbsp;cm by rain splashing into the cups.<ref name="Equihua-1987">{{cite journal |last1=Equihua |first1=C |title=Diseminacion de yemas en ''Marchantia polymorpha'' L. (Hepaticae) |trans-title=Dissemination of yolks in ''Marchantia polymorpha'' L. (Hepaticae) |language=fr |journal=Cryptogamie, Bryologie, Lichénologie |date=1987 |volume=8 |issue=3 |pages=199–217 |id={{INIST|8356670}} |url=https://www.biodiversitylibrary.org/page/60738107 }}</ref> In ''[[Metzgeria]]'', gemmae grow at thallus margins.<ref name="Lepp-Feb 2008">{{cite web | url=http://www.anbg.gov.au/bryophyte/sexual-vegetative.html | title=Reproduction & Dispersal | publisher=Australian National Botanic Gardens | work=Australian Bryophytes | date=28 February 2008 | access-date=December 22, 2011 | author=Lepp, Heino}}</ref> ''Marchantia polymorpha'' is a common weed in greenhouses, often covering the entire surface of containers;<ref name="Wehtje-2006"/>{{rp|230}} gemma dispersal is the "primary mechanism by which liverwort spreads throughout a nursery or greenhouse."<ref name="Wehtje-2006">{{cite journal |last1=Newby |first1=Adam |last2=Altland |first2=James E. |last3=Gilliam |first3=Charles H. |last4=Wehtje |first4=Glenn |title=Postemergence Liverwort Control in Container-Grown Nursery Crops |journal=Journal of Environmental Horticulture |date=December 2006 |volume=24 |issue=4 |pages=230–236 |doi=10.24266/0738-2898-24.4.230 }}</ref>{{rp|231}}

==== Symbiosis ====
Thalloid liverworts typically harbor symbiotic [[glomeromycete]] fungi which have arbuscular (cilia-bearing) rootlets resembling those in vascular plants. Species in the [[Aneuraceae]], however, associate with [[basidiomycete]] fungi belonging to the genus ''[[Tulasnella]]'', while leafy liverworts typically harbor symbiotic basidiomycete fungi belonging to the genus ''[[Serendipita]]''.<ref>{{cite journal |last1=Bidartondo |first1=Martin I. |last2=Duckett |first2=Jeffrey G. |title=Conservative ecological and evolutionary patterns in liverwort–fungal symbioses |journal=Proceedings of the Royal Society B: Biological Sciences |date=7 February 2010 |volume=277 |issue=1680 |pages=485–492 |doi=10.1098/rspb.2009.1458|pmid=19812075 |pmc=2842645 |bibcode=2010PBioS.277..485B }}</ref>

== 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'', vol. I, pp. 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", p. 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 ==

=== Evolution ===
[[Epiphytic]] thalloid liverworts evolved during the [[Triassic]] to the [[Cretaceous]].<ref>{{cite journal |last1=Bechteler |first1=Julia |last2=Schäfer-Verwimp |first2=Alfons |last3=Glenny |first3=David |last4=Cargill |first4=D. Christine |last5=Maul |first5=Karola |last6=Schütz |first6=Nicole |last7=von Konrat |first7=Matt |last8=Quandt |first8=Dietmar |last9=Nebel |first9=Martin |title=The evolution and biogeographic history of epiphytic thalloid liverworts |journal=Molecular Phylogenetics and Evolution |date=December 2021 |volume=165 |article-number=107298 |doi=10.1016/j.ympev.2021.107298 |pmid=34464738 |bibcode=2021MolPE.16507298B }}</ref>

=== 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 name="Schofield" /><ref>Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". pp. 36–38 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press: 2000). {{ISBN|0-521-66097-1}}</ref> Somewhat more recently, the liverworts were given their own division (Marchantiophyta),<ref>Goffinet, Bernard. "Origin and phylogenetic relationships of bryophytes". pp. 124–149 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press:!2000). {{ISBN|0-521-66097-1}}</ref> as bryophytes became considered to be [[paraphyly|paraphyletic]]. However, the most recent phylogenetic evidence indicates that liverworts are indeed likely part of a monophyletic clade ("Bryophyta ''sensu lato''" or "Bryophyta Schimp.") alongside mosses and hornworts.<ref name="Leebens-Mack-2019">{{cite journal |title=One thousand plant transcriptomes and the phylogenomics of green plants |last1=Leebens-Mack |first1=James H. |display-authors=etal |journal=Nature |volume=574 |pages=679–685 |year=2019 |issue=7780 |doi =10.1038/s41586-019-1693-2 |pmid=31645766 |pmc=6872490}}</ref><ref name="Harris-2020">{{cite journal |title=Phylogenomic Evidence for the Monophyly of Bryophytes and the Reductive Evolution of Stomata |last1=Harris |first1=Brogan J. |display-authors=etal |journal=Current Biology |volume=30 |issue=11 |pages=P2201–2012.E2 |year=2020 |doi=10.1016/j.cub.2020.03.048 |pmid=32302587 |bibcode=2020CBio...30E2001H |hdl=1983/fbf3f371-8085-4e76-9342-e3b326e69edd |hdl-access=free }}</ref><ref name="Su-2021">{{cite journal |title=Large-Scale Phylogenomic Analyses Reveal the Monophyly of Bryophytes and Neoproterozoic Origin of Land Plants |last1=Su |first1=Danyan |display-authors=etal |journal=Molecular Biology and Evolution |year=2021 |volume=38 |issue=8 |pages=3332–3344 |doi=10.1093/molbev/msab106 |pmid=33871608 |pmc=8321542}}</ref> Hence, it has been suggested that the liverworts should be de-ranked to a class called Marchantiopsida.<ref name="de Sousa-2019">{{cite journal |last1=de Sousa |first1=Filipe |display-authors=etal |year=2019 |title=Nuclear protein phylogenies support the monophyly of the three bryophyte groups (Bryophyta Schimp.) |journal=New Phytologist |volume=222 |issue=1 |pages=565–575 |bibcode=2019NewPh.222..565D |doi=10.1111/nph.15587 |pmid=30411803 |hdl-access=free |hdl=1983/0b471d7e-ce54-4681-b791-1da305d9e53b}}</ref> In addition, there is strong phylogenetic evidence to suggest that liverworts and mosses form a monophyletic subclade named [[Setaphyta]].<ref name="Puttick-2018">{{cite journal |last1=Puttick |first1=Mark N. |last2=Morris |first2=Jennifer L. |last3=Williams |first3=Tom A. |last4=Cox |first4=Cymon J. |last5=Edwards |first5=Dianne |last6=Kenrick |first6=Paul |last7=Pressel |first7=Silvia |last8=Wellman |first8=Charles H. |last9=Schneider |first9=Harald |last10=Pisani |first10=Davide |last11=Donoghue |first11=Philip C.J. |display-authors=1 |date=March 2018 |title=The Interrelationships of Land Plants and the Nature of the Ancestral Embryophyte |journal=Current Biology |volume=28 |issue=5 |pages=733–745.e2 |bibcode=2018CBio...28E.733P |doi=10.1016/j.cub.2018.01.063 |pmid=29456145 |hdl-access=free |hdl=1983/ad32d4da-6cb3-4ed6-add2-2415f81b46da}}</ref><ref name="Sousa-2020">{{cite journal |title=The mitochondrial phylogeny of land plants shows support for Setaphyta under composition-heterogeneous substitution models |last1=Sousa |first1=Filipe |display-authors=etal |journal=PeerJ |year=2020 |volume=8 |issue=4 |article-number=e8995 |doi=10.7717/peerj.8995|pmid=32377448 |pmc=7194085 |doi-access=free }}</ref><ref name="Cox-2018">{{cite journal |title=Land Plant Molecular Phylogenetics: A Review with Comments on Evaluating Incongruence Among Phylogenies |journal=Critical Reviews in Plant Sciences |last=Cox |first=Cymon J. |volume=37 |issue=2–3 |pages=113–127 |year=2018 |doi=10.1080/07352689.2018.1482443|bibcode=2018CRvPS..37..113C |hdl=10400.1/14557 |hdl-access=free }}</ref>
{| cellpadding=5 style="border:1px solid #BBB" cellpadding=10;
! 'Monophyletic bryophytes' model
! 'Liverworts plus mosses{{en dash}}basal' model
|-
|{{Clade|style=line-height:100%;
|label1=[[embryophyte]]s
|1={{Clade
   |1=[[vascular plant]]s
   |label2=[[bryophyte]]s
   |2={{clade
      |1=[[hornwort]]s
      |label2=[[Setaphyta|setaphytes]]
      |2={{clade
         |1=[[moss]]es
         |2=[[liverwort]]s
         }}
      }}
   }}
}}
|{{Barlabel
|size=4
|at1=2
|cladogram=
{{Clade
|label1=embryophytes
|1={{Clade
   |1={{Clade
      |1=[[vascular plants]]
      |2=[[hornworts]]
      }}
   |label2=[[Setaphyta|setaphytes]]
   |2={{Clade
      |1=[[mosses]]
      |2=[[liverworts]]
      }}
   }}
}}
}}
|-
| colspan="2"|Two of the most likely models for bryophyte evolution.<ref name="Cox-2018"/>
|}

An important conclusion from these phylogenies is that the ancestral stomata appear to have been lost in the liverwort lineage.<ref name="Puttick-2018"/><ref name="Harris-2020"/> Among the earliest [[fossil]]s believed to be liverworts are [[compression fossil]]s of ''[[Pallaviciniites]]'' from the Upper [[Devonian]] of [[New York (state)|New York]].<ref>Taylor, Thomas N. & Edith L. Taylor. ''The Biology and Evolution of Fossil Plants'', p. 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'', pp. 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 at that time to the liverworts were announced, ''Metzgeriothallus sharonae'' from the [[Givetian]] (Middle [[Devonian]]) of [[New York (state)|New York]], United States.<ref name="VanAller Hernick-2008">{{cite journal
| last = VanAller Hernick | first = L. |author2=Landing, E. |author3=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
| issue = 2–4
|pages=154–162
| journal = Review of Palaeobotany and Palynology | bibcode = 2008RPaPa.148..154H }}</ref> However, in 2010, five different types of fossilized liverwort spores were found in Argentina, dating to the much earlier Middle [[Ordovician]], around 470 million years ago.<ref name="Walker-2010">{{Cite news |last=Walker |first=Matt |date=October 12, 2010 |title=Fossils of earliest land plants discovered in Argentina |url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_9079000/9079963.stm |access-date=2025-09-20 |work=BBC Earth |language=en-GB}}</ref><ref>{{Cite journal |last1=Rubinstein |first1=C. V. |last2=Gerrienne |first2=P. |last3=De La Puente |first3=G. S. |last4=Astini |first4=R. A. |author5=Steemans, P. |year=2010 |title=Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana) |journal=New Phytologist |volume=188 |issue=2 |pages=365–369 |doi=10.1111/j.1469-8137.2010.03433.x |pmid=20731783 |doi-access=free |bibcode=2010NewPh.188..365R |hdl=11336/55341 |hdl-access=free }}</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". p. 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 is not to be mistakenly associated with [[flowering plant]] genus ''[[Hepatica]]'', of the buttercup family [[Ranunculaceae]]. In addition, the name Hepaticophyta is frequently misspelled in textbooks as '''Hepatophyta.'''

Although there is no consensus among bryologists as to the classification of liverworts above family rank,<ref>{{Cite book| last=Jones | first=E. W. | year=2004 | title=Liverwort and Hornwort Flora of West Africa | series=Scripta Botnica Belgica | volume=30 | location=Meise | publisher=National Botanic Garden (Belgium) | isbn=90-72619-61-7 | page=30 }}</ref> the Marchantiophyta may be subdivided into three classes:<ref name="Forrest-2006">{{cite journal |last1=Forrest |first1=Laura L. |last2=Davis |first2=E. Christine |last3=Long |first3=David G. |last4=Crandall-Stotler |first4=Barbara J. |last5=Clark |first5=Alexandra |last6=Hollingsworth |first6=Michelle L. |title=Unraveling the evolutionary history of the liverworts (Marchantiophyta): Multiple taxa, genomes and analyses |journal=The Bryologist |date=2006 |volume=109 |issue=3 |page=303 |doi=10.1639/0007-2745(2006)109[303:UTEHOT]2.0.CO;2 }}</ref><ref name="Heinrichs-2005">{{cite journal |last1=He-Nygrén |first1=Xiaolan |last2=Juslén |first2=Aino |last3=Ahonen |first3=Inkeri |last4=Glenny |first4=David |last5=Piippo |first5=Sinikka |title=Illuminating the evolutionary history of liverworts (Marchantiophyta)—towards a natural classification |journal=Cladistics |date=2006 |volume=22 |issue=1 |pages=1–31 |doi=10.1111/j.1096-0031.2006.00089.x |pmid=34892891 }}</ref><ref name="Renzaglia-2007">{{cite journal |last1=Renzaglia |first1=Karen S. |last2=Schuette |first2=Scott |last3=Duff |first3=R. Joel |last4=Ligrone |first4=Roberto |last5=Shaw |first5=A. Jonathan |last6=Mishler |first6=Brent D. |last7=Duckett |first7=Jeffrey G. |title=Bryophyte phylogeny: Advancing the molecular and morphological frontiers |journal=The Bryologist |date=2007 |volume=110 |issue=2 |page=179 |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" /><ref name="Forrest-2004">{{cite journal | last=Forrest | first=Laura L. |author2=Barbara J. Crandall-Stotler | year=2004 | title=A Phylogeny of the Simple Thalloid Liverworts (Jungermanniopsida, Metzgeriidae) as Inferred from Five Chloroplast Genes | series=Molecular Systematics of Bryophytes | journal=Monographs in Systematic Botany | volume=98 | pages=119–140 | publisher= Missouri Botanical Garden Press }}</ref> 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'', vol. VI, p. 26. (Chicago: Field Museum of Natural History, 1992). {{ISBN|0-914868-21-7}}.</ref>
* A third class, the '''[[Haplomitriopsida]]''' is newly recognized as the sister group of the other liverworts;<ref name="Renzaglia-2007" /> it comprises the genera ''[[Haplomitrium]]'', ''[[Treubia]]'', and ''[[Apotreubia]]''.

{| class="wikitable"
|-
! colspan=1 | Forrest 2006<ref name="Forrest-2006"/>
! colspan=1 | Cole, Hilger & Goffinet 2021 <ref>{{cite web |title=Bryophyte phylogeny poster: systematics and Characteristics of Nonvascular Land Plants (Mosses, Liverworts, Hornworts) |last1=Cole |first1=Theodor C. H. |last2=Hilger |first2=Hartmut H. |last3=Goffinet |first3=Bernard |url=https://www.researchgate.net/publication/257240194 |version=2021 |access-date=6 December 2022}}</ref>
|- 
| style="vertical-align:top|
{{Clade | style=font-size:90%;line-height:80%
|label1=Marchantiophyta
|1={{clade
  |1={{clade
    |label1=[[Haplomitriopsida]]
    |1={{clade
      |1=[[Haplomitriales]]
      |2=[[Treubiales]]
       }}
     }}
  |2={{clade
    |label1=Marchantiopsida
    |1={{clade
      |1=[[Blasiales]]
      |2={{clade
        |1=[[Marchantiales]]
        |2=[[Sphaerocarpales]]
         }}
       }}
    |label2=Jungermanniopsida
    |2={{clade
      |1=[[Metzgeriales]] (part)
      |2={{clade
        |1=[[Metzgeriales]] (part)
        |2=[[Jungermanniales]]
         }}
       }}
     }}
   }}
}}
|
{{Clade | style=font-size:90%;line-height:80%
|1={{clade
  |1={{clade
    |label1=[[Haplomitriopsida]]
    |1={{clade
      |1=[[Haplomitriales]]
      |2=[[Treubiales]]
       }}
     }}
  |2={{clade
    |label1=[[Marchantiopsida]]
    |1={{clade
      |label1=Blasiidae
      |1=[[Blasiales]]
      |label2=Marchantiidae
      |2={{clade
        |1=[[Neohodgsoniales]]
        |2={{clade
          |1=[[Sphaerocarpales]]
          |2={{clade
            |1=[[Lunulariales]]
            |2=[[Marchantiales]]
             }}
           }}
         }}
       }}
    |label2=[[Jungermanniopsida]]
    |2={{clade
      |1={{clade
        |label1=Pelliidae
        |1={{clade
          |1=[[Pelliales]]
          |2={{clade
            |1=[[Fossombroniales]]
            |2=[[Pallaviciniales]]
             }}
           }}
         }}
      |2={{clade
        |label1=Metzgeriidae
        |1={{clade
          |1=[[Metzgeriales]]
          |2=[[Pleuroziales]]
           }}
        |label2=Jungermanniidae
        |2={{clade
          |1=[[Jungermanniales]]
          |2={{clade
            |1=[[Porellales]]
            |2=[[Ptilidiales]]
             }}
           }}
         }}
       }}
     }}
   }}
}}
|}

An updated classification by Söderström et al. 2016<ref name="Söderström-2016">{{cite journal |last=Söderström |year=2016 |title=World checklist of hornworts and liverworts |journal=PhytoKeys |issue=59 |pages=1–826 |doi=10.3897/phytokeys.59.6261|display-authors=etal |pmid=26929706 |pmc=4758082 |doi-access=free |bibcode=2016PhytK..59....1S }}</ref>
* '''Marchantiophyta''' <small>Stotler & Crandall-Stotler 2000</small>
** [[Haplomitriopsida]] <small>Stotler & Crandall-Stotler 1977</small>
*** [[Calobryales]] <small>Hamlin 1972</small>
*** [[Treubiales]] <small>Schljakov 1972</small>
** [[Marchantiopsida]] <small>Cronquist, Takhtajan & Zimmermann 1966</small>
*** [[Blasiidae]] <small>He-Nygrén et al. 2006</small>
**** [[Blasiales]] <small>Stotler & Crandall-Stotler 2000</small>
*** [[Marchantiidae]] <small>Engler 1893 sensu He-Nygrén et al. 2006</small>
**** [[Lunulariales]] <small>Long 2006</small>
**** [[Marchantiales]] <small>Limpricht 1877</small> (complex thalloids)
**** [[Neohodgsoniales]] <small>Long 2006</small>
**** [[Sphaerocarpales]] <small>Cavers 1910</small> (bottle liverworts)
** [[Jungermanniopsida]] <small>Stotler & Crandall-Stotler 1977</small>
*** [[Jungermanniidae]] <small>Engler 1893</small> (leafy liverworts)
**** [[Jungermanniales]] <small>von Klinggräff 1858</small>
**** [[Porellales]] <small>Schljakov 1972</small>
**** [[Ptilidiales]] <small>Schljakov 1972</small>
*** [[Metzgeriidae]] <small>Bartholomew-Began 1990</small>
**** [[Metzgeriales]] <small>Chalaud 1930</small>
**** [[Pleuroziales]] <small>Schljakov 1972</small>
*** [[Pelliidae]] <small>He-Nygrén et al. 2006</small>
**** [[Fossombroniales]] <small>Schljakov 1972</small>
**** [[Pallaviciniales]] <small>Frey & Stech 2005</small>
**** [[Pelliales]] <small>He-Nygrén et al. 2006</small>

It is estimated that there are about 9000 species of liverworts, at least 85% of which belong to the leafy group.<ref name="Crandall-Stotler-2000" /><ref name="Sadava-2009">{{cite book|last=Sadava|first=David|title=Life: The Science of Biology|year=2009|publisher=W. H. Freeman|location=New York|isbn=978-1429246446|edition=9th|author2=David M. Hillis |author3=H. Craig Heller |author4=May Berenbaum |page=599}}</ref> Despite that fact, no liverwort genomes have been sequenced to date and only few genes identified and characterized.<ref>{{Cite journal| pmid=24939387| pmc=4074843| year=2014
| last1 = Sierocka| first1 = I| title = Female-specific gene expression in dioecious liverwort Pellia endiviifolia is developmentally regulated and connected to archegonia production| journal = BMC Plant Biology| volume = 14| pages = 168| last2 = Kozlowski| first2 = L. P.| last3 = Bujnicki
| first3 = J. M.| last4 = Jarmolowski| first4 = A| last5 = Szweykowska-Kulinska| first5 = Z| issue=1| doi = 10.1186/1471-2229-14-168| doi-access=free| bibcode=2014BMCPB..14..168S}}</ref>

==== Extinct taxa ====
There are several known [[Fossil taxa|fossil genera]] from this group that are not assigned to any extant class:<ref>{{Cite web |title=PBDB Taxon |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=306729&is_real_user=1 |access-date=2025-01-18 |website=paleobiodb.org}}</ref>

* †''Discites'' ''<small>[[Tom Harris (botanist)|Harris]] 1931</small>''
* †''Eohepatica'' ''<small>Heard and Jones 1931</small>''
* †''Jungermanniopsis'' ''<small>[[Marshall Avery Howe|Howe]] and [[Arthur Hollick|Hollick]] 1922</small>''
* †''Jungermannites'' ''<small>[[Heinrich Göppert|Göppert]] 1845</small>''
* †''Schizolepidella'' ''<small>Halle 1913</small>''
* †''Thallomia'' ''<small>Heard and Jones 1931</small>''

==Economic importance==
In ancient times, it was assumed that liverworts cured diseases of the [[liver]], hence the name.<ref>Dittmer, Howard J. ''Phylogeny and Form in the Plant Kingdom'', p. 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., p. 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., p. 338. (Dubuque, Iowa: Wm. C. Brown Publishers, 1991) {{ISBN|0-697-09947-4}}.</ref>

Liverworts have little direct economic importance today. Their greatest impact is indirect, through 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]]s. 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 class=center mode=nolines widths=175px heights=175px>
File:Marchantia.jpg|''[[Marchantia]] polymorpha'', with antheridial and archegonial stalks
File:Archegonium.jpg|The [[archegonium]] of ''Porella''
File:Porella SPT.jpg|A sporophyte of ''Porella'' emerging from its archegonium
File:Porella platyphylla.jpg|''[[Porella]] platyphylla'' clump growing on a tree
File:Pellia epiphylla5 ies.jpg|''[[Pellia]] epiphylla'', growing on moist soil
File:Plagiochila aspleniodes0.jpg|''[[Plagiochila]] asplenioides'', a [[Jungermanniales|leafy liverwort]]
File:RicciaFluitans1.jpg|''[[Riccia fluitans]]'', an aquatic [[Marchantiales|thallose liverwort]]
File:Liverwort.jpg|''[[Conocephalum]] conicum'', a large thallose liverwort
</gallery>

== See also ==
* [[Bryophyte]]
* [[Embryophyte]]

== References ==
{{Reflist|2}}

== External links ==
{{Wiktionary|liverwort}}
* {{Commons category-inline|Marchantiophyta}}
* {{Wikispecies-inline|Marchantiophyta}}
* [https://web.archive.org/web/20050323090944/http://www2.una.edu/pdavis/hepatic_orders.htm Liverwort structure in pictures]
* [https://web.archive.org/web/20070831024018/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".)
* [https://web.archive.org/web/20050413214451/http://www.bio.ilstu.edu/armstrong/syllabi/222book/chapt6.htm Inter-relationships of Mosses, Liverworts, and Hornworts]
* [https://web.archive.org/web/20051025142835/http://www.bio.umass.edu/biology/conn.river/liverwts.html Additional information on Liverworts]
* [https://web.archive.org/web/20050303043539/http://www.hcs.ohio-state.edu/hcs300/liver1.htm Liverworts]

{{Plant classification}}
{{Marchantiophyta}}
{{Life on Earth}}
{{Taxonbar|from=Q189808}}
{{Authority control}}
{{Good article}}

[[Category:Liverworts| ]]
[[Category:Plant divisions]]
[[Category:Early Ordovician first appearances]]
[[Category:Extant Ordovician first appearances]]
[[Category:Bryophytes]]