Liverworts are a group of
non-vascular land plant
The embryophytes () are a clade of plants, also known as Embryophyta (Plantae ''sensu strictissimo'') () or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophyt ...
s forming the division Marchantiophyta (). They may also be referred to as hepatics. Like
mosses
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ho ...
and
hornworts
Hornworts are a group of Non-vascular plant, non-vascular Embryophytes (land plants) constituting the division Anthocerotophyta (). The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts ...
, they have a
gametophyte
A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the se ...
-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
''Marchantia'' is a genus of liverworts in the family Marchantiaceae and the order Marchantiales. The genus was named by French botanist Jean Marchant after his father.
The thallus of ''Marchantia'' shows differentiation into two layers: an ...
'', named after his father by French botanist
Jean Marchant.
It is estimated that there are about 9000 species of liverworts. Some of the more familiar species grow as a flattened leafless
thallus
Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...
, but most species are leafy with a form very much like a flattened
moss
Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
. Leafy species can be distinguished from the apparently similar mosses on the basis of a number of features, including their single-celled
rhizoid
Rhizoids are protuberances that extend from the lower epidermal cells of bryophytes and algae. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by some fungi. Rhizoids may be un ...
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
The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...
(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 wide with individual plants less than 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.
Physical characteristics
Description
Most liverworts are small, measuring from wide with individual plants less than long, so they are often overlooked. The most familiar liverworts consist of a prostrate, flattened, ribbon-like or branching structure called a
thallus
Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...
(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 ''
leafy liverworts'' or ''scale liverworts''.
[Schofield, W. B. ''Introduction to Bryology'', pp. 135–140. (New York: Macmillan, 1985). .] (''See the
gallery
Gallery or The Gallery may refer to:
* Gallery (surname), a surname
Arts, entertainment, and media
* Art gallery
** Contemporary art gallery
** Online art gallery
Music
* Gallery (band), an American soft rock band of the 1970s
Albums
* ' ...
below for examples.'')
Liverworts can most reliably be distinguished from the apparently similar
moss
Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
es by their single-celled
rhizoid
Rhizoids are protuberances that extend from the lower epidermal cells of bryophytes and algae. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by some fungi. Rhizoids may be un ...
s. Other differences are not universal for all mosses and all liverworts;
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, 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. Unlike any other embryophytes, most liverworts contain
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.
[Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. ''Morphology of Plants and Fungi'', 5th ed., p. 189. (New York: Harper-Collins, 1987). .] 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
Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical mic ...
or an experienced
bryologist.
Liverworts, like other bryophytes, have a
gametophyte
A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the se ...
-dominant life cycle, with the
sporophyte
A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...
dependent on the gametophyte.
The sporophyte of many liverworts are non-photosynthetic, but there are also several that are photosynthetic to various degrees. Cells in a typical liverwort plant each contain only a single set of genetic information, so the plant's cells are
haploid
Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...
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
A seed plant or spermatophyte (; New Latin ''spermat-'' and Greek ' (phytón), plant), also known as a phanerogam (taxon Phanerogamae) or a phaenogam (taxon Phaenogamae), is any plant that produces seeds. It is a category of embryophyte (i.e. la ...
s, the haploid generation is represented only by the tiny
pollen
Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...
and the
ovule
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the sporangium, megasporangium), ...
, while the
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...
generation is the familiar tree or other plant. Another unusual feature of the liverwort life cycle is that sporophytes (i.e. the
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...
body) are very short-lived, withering away not long after releasing spores. In mosses, the sporophyte is more persistent and in hornworts, the sporophyte disperses spores over an extended period.
Life cycle
The life of a liverwort starts from the germination of a haploid
spore
In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
to produce a
protonema
A protonema (plural: protonemata) is a thread-like chain of cells that forms the earliest stage of development of the gametophyte (the haploid phase) in the life cycle of mosses. When a moss first grows from a spore, it starts as a ''germ tube'', ...
, which is either a mass of thread-like filaments or a flattened thallus. The protonema is a transitory stage in the life of a liverwort, from which will grow the mature gametophore ("
gamete
A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...
-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
An archegonium (: archegonia), from the Ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamet ...
(''singular:'' archegonium) and are protected by the thin surrounding perichaetum (''plural:'' perichaeta).
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
Dioicy () is a sexual system in non-vascular plants where archegonia (female organs) and antheridia (male organs) are produced on separate plants in the gametophyte phase. It is one of the two main sexual systems in bryophytes, the other being ...
or
monoicous
Monoicy () is a sexual system in haploid plants (mainly bryophytes) where both sperm and eggs are produced on the same gametophyte, in contrast with dioicy, where each gametophyte produces only sperm or eggs but never both.Crandall-Stotler, B.J ...
. 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. In either case, the sperm must move from the antheridia where they are produced to the archegonium where the eggs are held. The
sperm
Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm ...
of liverworts is ''biflagellate'', i.e. they have two tail-like
flagellae that enable them to swim short distances,
[Campbell, Douglas H. ''The Structure and Development of Mosses and Ferns'', pp. 73–74. (London: The Macmillan Co., 1918)](_blank)
/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 cm in the air, enabling them to fertilize female plants growing more than a metre from the nearest male.
When sperm reach the archegonia, fertilisation
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a zygote and initiate its development into a new individual organism or of ...
occurs, leading to the production of a diploid sporophyte. After fertilisation, the immature sporophyte
A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...
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. The sporophyte lacks an apical meristem
In cell biology, the meristem is a structure composed of specialized tissue found in plants, consisting of stem cells, known as meristematic cells, which are undifferentiated cells capable of continuous cellular division. These meristematic ce ...
, an auxin
Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essent ...
-sensitive point of divergence with other land plants some time in the Late Silurian
The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
/Early Devonian
The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...
. 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
An elater is a cell (or structure attached to a cell) that is hygroscopic, and therefore will change shape in response to changes in moisture in the environment. Elaters come in a variety of forms, but are always associated with plant spores. In ...
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
Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...
to form haploid spore
In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
s to disperse, upon which point the life cycle can start again.
Asexual reproduction
Some liverworts are capable of asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...
; in bryophytes in general "it would almost be true to say that vegetative reproduction is the rule and not the exception." For example, in ''Riccia
''Riccia'' is a genus of liverworts in the order Marchantiales.
Description
These plants are small and thalloid, i.e. not differentiated into root, stem and leaf. Depending on species, the thallus may be strap-shaped and about 0.5 to 4 m ...
'', when the older parts of the forked thalli die, the younger tips become separate individuals.
Some thallose liverworts such as ''Marchantia polymorpha
''Marchantia polymorpha'' is a species of large thalloid liverwort in the class Marchantiopsida. ''M. polymorpha'' is highly variable in appearance and contains several subspecies. This species is dioicous, having separate male and female plants. ...
'' and '' Lunularia cruciata'' produce small disc-shaped gemmae in shallow cups. ''Marchantia'' gemmae can be dispersed up to 120 cm by rain splashing into the cups. In '' Metzgeria'', gemmae grow at thallus margins. ''Marchantia polymorpha'' is a common weed in greenhouses, often covering the entire surface of containers; gemma dispersal is the "primary mechanism by which liverwort spreads throughout a nursery or greenhouse."
Symbiosis
Thalloid liverworts typically harbor symbiotic glomeromycete fungi which have arbuscular (cilia-bearing) rootlets resembling those in vascular plants. Species in the Aneuraceae
Aneuraceae (sometimes Riccardiaceae) is a family of thallose liverworts in the order Metzgeriales. Most species are very small with narrow, branching thalli.
Taxonomy
Aneuraceae is the largest family in the order Metzgeriales, simple thalloid ...
, however, associate with basidiomycete
Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basid ...
fungi belonging to the genus ''Tulasnella
''Tulasnella'' is a genus of effused (patch-forming) fungi in the order Cantharellales. Basidiocarps (fruit bodies), when visible, are typically smooth, ceraceous (waxy) to subgelatinous, frequently lilaceous to violet-grey, and formed on the und ...
'', while leafy liverworts typically harbor symbiotic basidiomycete fungi belonging to the genus ''Serendipita
''Serendipita'' is a genus in the family Serendipitaceae. The type species, ''Serendipita vermifera'', was first described by Oberwinkler in 1964 (originally ''Sebacina vermifera''). There is a large molecular diversity, but the absence of macro ...
''.
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. As with most groups of living plants, they are most common (both in numbers and species) in moist tropical areas. 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
Bryophytes () are a group of embryophyte, land plants (embryophytes), sometimes treated as a taxonomic Division (taxonomy), division referred to as Bryophyta ''Sensu#Common qualifiers, sensu lato'', that contains three groups of non-vascular pla ...
s (moss
Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
es and hornwort
Hornworts are a group of non-vascular Embryophytes (land plants) constituting the division Anthocerotophyta (). The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts, hornworts have a ...
s) in the Division Bryophyta, within which the liverworts made up the class Hepaticae (also called Marchantiopsida). Somewhat more recently, the liverworts were given their own division (Marchantiophyta), as bryophytes became considered to be paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
. 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. Hence, it has been suggested that the liverworts should be de-ranked to a class called Marchantiopsida. In addition, there is strong phylogenetic evidence to suggest that liverworts and mosses form a monophyletic subclade named Setaphyta.
An important conclusion from these phylogenies is that the ancestral stomata appear to have been lost in the liverwort lineage.[ Among the earliest ]fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s believed to be liverworts are compression fossil
A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. While it is uncommon to find animals preserved as good compression fossils, it is very common to find plants preserved this way. The reason f ...
s of '' Pallaviciniites'' from the Upper Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
of New York
New York most commonly refers to:
* New York (state), a state in the northeastern United States
* New York City, the most populous city in the United States, located in the state of New York
New York may also refer to:
Places United Kingdom
* ...
. These fossils resemble modern species in the Metzgeriales
Metzgeriales is an order of liverworts. The group is sometimes called the simple thalloid liverworts: " thalloid" because the members lack structures resembling stems or leaves, and "simple" because their tissues are thin and relatively undiff ...
. 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
The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian Stage. It is named after the town of Givet in ...
(Middle Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
) of New York
New York most commonly refers to:
* New York (state), a state in the northeastern United States
* New York City, the most populous city in the United States, located in the state of New York
New York may also refer to:
Places United Kingdom
* ...
, United States. However, in 2010, five different types of fossilized liverwort spores were found in Argentina, dating to the much earlier Middle Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
, around 470 million years ago.[Walker, Matt. "Fossils of earliest land plants discovered in Argentina]
(BBC, Earth News, 2010).
Internal classification
Bryology, Bryologists classify liverworts in the division Marchantiophyta. This divisional name is based on the name of the most universally recognized liverwort genus ''Marchantia
''Marchantia'' is a genus of liverworts in the family Marchantiaceae and the order Marchantiales. The genus was named by French botanist Jean Marchant after his father.
The thallus of ''Marchantia'' shows differentiation into two layers: an ...
''. In addition to this taxon
In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
-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
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
genus '' Hepatica'', of the buttercup family Ranunculaceae
Ranunculaceae (, buttercup or crowfoot family; Latin "little frog", from "frog") is a family (biology), family of over 2,000 known species of flowering plants in 43 genera, distributed worldwide.
The largest genera are ''Ranunculus'' (600 spec ...
. 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, the Marchantiophyta may be subdivided into three classes:
* The Jungermanniopsida includes the two orders
Order, ORDER or Orders may refer to:
* A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* H ...
Metzgeriales
Metzgeriales is an order of liverworts. The group is sometimes called the simple thalloid liverworts: " thalloid" because the members lack structures resembling stems or leaves, and "simple" because their tissues are thin and relatively undiff ...
(simple thalloids) and Jungermanniales
Jungermanniales is the largest Order (biology), order of Marchantiophyta, liverworts. They are distinctive among the liverworts for having thin leaf-like flaps on either side of the stem. Most other liverworts are thalloid, with no leaves. Due to ...
(leafy liverworts).
* The Marchantiopsida includes the three orders Marchantiales
Marchantiales is an order of thallose liverworts (also known as "complex thalloid liverworts") that includes species like '' Marchantia polymorpha'', a widespread plant often found beside rivers, and '' Lunularia cruciata'', a common and often t ...
(complex-thallus liverworts), and Sphaerocarpales (bottle hepatics), as well as the Blasiales
Blasiales is an order of liverworts with a single living family and two species. The order has traditionally been classified among the Metzgeriales, but molecular cladistics suggests a placement at the base of the Marchantiopsida.
Taxonomy
* Bl ...
(previously placed among the Metzgeriales). It also includes the problematic genus ''Monoclea
''Monoclea'' is a genus of liverwort that contains two species. It is the only genus in the family Monocleaceae. Species of this genus can be found in New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. ...
'', which is sometimes placed in its own order Monocleales.
* A third class, the Haplomitriopsida
Haplomitriopsida is a Class (biology), class of Marchantiophyta, liverworts comprising fifteen species in three genus, genera. Recent cladistics, cladistic analyses of cell nucleus, nuclear, mitochondrial, and plastid gene sequences place this mo ...
is newly recognized as the sister group of the other liverworts; it comprises the genera '' Haplomitrium'', '' Treubia'', and '' Apotreubia''.
An updated classification by Söderström et al. 2016
* Marchantiophyta Stotler & Crandall-Stotler 2000
** Haplomitriopsida
Haplomitriopsida is a Class (biology), class of Marchantiophyta, liverworts comprising fifteen species in three genus, genera. Recent cladistics, cladistic analyses of cell nucleus, nuclear, mitochondrial, and plastid gene sequences place this mo ...
Stotler & Crandall-Stotler 1977
*** Calobryales
Calobryales (formerly Haplomitriales) is an order of plants known as liverworts.
This order contains one family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), aff ...
Hamlin 1972
*** Treubiales Schljakov 1972
** Marchantiopsida
Marchantiopsida is a class of liverworts within the phylum Marchantiophyta. The species in this class are known as complex thalloid liverworts. The species in this class are widely distributed and can be found worldwide. Complex oil bodies are on ...
Cronquist, Takhtajan & Zimmermann 1966
*** Blasiidae
Blasiales is an order (biology), order of Marchantiophyta, liverworts with a single living family (biology), family and two species. The order has traditionally been classified among the Metzgeriales, but molecular cladistics suggests a placement ...
He-Nygrén et al. 2006
**** Blasiales
Blasiales is an order of liverworts with a single living family and two species. The order has traditionally been classified among the Metzgeriales, but molecular cladistics suggests a placement at the base of the Marchantiopsida.
Taxonomy
* Bl ...
Stotler & Crandall-Stotler 2000
*** Marchantiidae Engler 1893 sensu He-Nygrén et al. 2006
**** Lunulariales
''Lunularia'' is a genus of liverworts whose only species is ''Lunularia cruciata'', the crescent-cup liverwort. ''Lunularia'' is either the only genus in the order Lunulariales, or may be placed in the order Marchantiales. The name, from Latin ...
Long 2006
**** Marchantiales
Marchantiales is an order of thallose liverworts (also known as "complex thalloid liverworts") that includes species like '' Marchantia polymorpha'', a widespread plant often found beside rivers, and '' Lunularia cruciata'', a common and often t ...
Limpricht 1877 (complex thalloids)
**** Neohodgsoniales Long 2006
**** Sphaerocarpales Cavers 1910 (bottle liverworts)
** Jungermanniopsida
Jungermanniopsida is the largest of three classes within the division Marchantiophyta (liverworts).
Phylogeny
Based on the work by Novíkov & Barabaš-Krasni 2015.
Taxonomy
* Jungermanniidae Engler 1893
** Jungermanniales von Klinggräff 185 ...
Stotler & Crandall-Stotler 1977
*** Jungermanniidae
Jungermanniopsida is the largest of three classes within the division Marchantiophyta (liverworts).
Phylogeny
Based on the work by Novíkov & Barabaš-Krasni 2015.
Taxonomy
* Jungermanniidae Engler 1893
** Jungermanniales von Klinggräff 185 ...
Engler 1893 (leafy liverworts)
**** Jungermanniales
Jungermanniales is the largest Order (biology), order of Marchantiophyta, liverworts. They are distinctive among the liverworts for having thin leaf-like flaps on either side of the stem. Most other liverworts are thalloid, with no leaves. Due to ...
von Klinggräff 1858
**** Porellales
Porellales is an order of liverworts.
Taxonomy
* Jubulineae Müller 1909
** Frullaniaceae Lorch 1914
*** '' Frullania'' Raddi 1818a Schljakov 1972
**** Ptilidiales">'Amphijubula'' Schuster 1970a; ''Schusterella'' Hattori, Sharp & Mizutani 1972; ''Steerea'' Hattori & Kamimu ...
It is estimated that there are about 9000 species of liverworts, at least 85% of which belong to the leafy group.
Despite that fact, no liverwort genomes have been sequenced to date and only few genes identified and characterized.
, hence the name. In
, the word liverwort literally means ''liver plant''. 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
word ''hēpaticus'' for "belonging to the liver". An unrelated flowering plant, ''
'', 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
.
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
s in deserts and polar regions. However, a few species are used by humans directly. A few species, such as ''
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.