Liverworts - Top Future Point

Marchantiophyta about this soundare a division of non-vascular land plants commonly referred to as hepatis or liverworts . Like mosses and hornworts , they have a gametophyte -dominant life cycle, in which plant cells carry only one set of genetic information.

It is estimated that there are about 9000 species of liverworts. [4] Some of the more familiar species develop a flattened leafless thallus, but most species are leafy, resembling a flattened moss. Leafy species can be clearly distinguished from similar mosses based on several characteristics, including their single-celled rhizoids. Leafy liverworts also differ from most (but not all) mosses in that their leaves never have costa (present in many mosses) and may have marginal cilia (very rare in mosses). Other differences are not universal to all mosses and liverworts, but the occurrence of leaves arranged in three ranks, the presence of deeply lobed or segmented leaves, or the lack of a clearly differentiated stem and leaves all point to the plant being a liverwort.

Liverworts are usually small, usually 2–20 mm wide and with individual plants less than 10 cm long, and are therefore often overlooked. However, some species can 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, mostly in humid places although there are also desert and arctic species. Some species can be a nuisance to weeds in shady greenhouses or gardens.

physical features

description

Most liverworts are small, measuring 2–20 millimeters (0.08–0.8 in) wide and individual plants less than 10 cm (4 in) tall, ^[6] so they are often overlooked. . The most familiar liverworts have a prostrate, flattened, ribbon-like or branched structure called a thallus (plant body); These liverworts are called thallos liverworts . Although most liverworts produce flattened stems with overlapping scales or leaves in two or more ranks, the middle rank is often clearly distinguished from the outer ranks; These are called leafy liverworts or scale liverworts . ^[7] [8] ( for example given belowView gallery .

Liverworts can be distinguished most reliably from apparently similar mosses by their single-celled rhizoids. ^[9] Other differences are not universal to all mosses and all liverworts; ^[8] But the lack of clearly differentiated stems and leaves in thallos species or in deciduous 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. ^[10]^[11] Unlike any other embryo, most liverworts have unique membrane-bound oil bodies that contain isoprenoids in at least some cells, with lipid droplets not sealed in the cytoplasm of all other plants. . ^[12]The overall physical similarity of some moss and leafy liverworts means that the identities of some groups can only be confirmed by microscopy or with the aid of an experienced biologist.

Liverworts, like other bryophytes, have a gametophyte -dominant life cycle, with the sporophyte dependent on the gametophyte. ^[12] The cells of a typical liverwort plant each contain only one set of genetic information, so the plant cells are haploid for most of their life cycle. This contrasts sharply with the pattern displayed by almost all animals and vascular plants. In the more familiar seed plants, the haploid generation is represented by only small pollen and ovules, while the diploid generation is the familiar tree or other plant. ^[13] Another unusual feature of the life cycle of the liverwort is that the sporophytes (ie diploid bodies) are very short-lived, dying shortly after releasing the spores. ^[14]In mosses, the sporophyte is more permanent and in hornworts, the sporophyte disperses spores over an extended period.

Life Cycle

The life of a liverwort begins from the germination of a haploid spore to produce a protonema, which is either a mass of thread-like filaments or a flattened thallus. ^[15]^[16] The protonema is a temporary stage in the life of a liverwort, from which will grow the mature gametophore (“gamete-bearer”) plant that produces sex organs. The male organs are known as antheridia ( singular: antheridium) and produce sperm cells. Clusters of antheridia are surrounded by a protective layer of cells called perigonium ( plural: perigonia). Like other land plants, the female organs are called archegonia ( singular:archegonium) and are protected by a thin surrounding perichatum ( plural: perichaeta). ^[8] Each archegonium has a thin hollow tube, the “neck”, below which sperm swim to reach the egg cell.

Liverwort species can be either dioicous or monoicous. In dioecious liverworts, female and male sex organs are produced separately and on separate gametophyte plants. In monoecious liverworts, the two types of reproductive structures are borne on different branches of the same plant. ^{[17] In} any case, sperm must move from the antheridia, where they are produced, to where the eggs are laid. Sperm of liverworts is biflagellate , ie they have two tail-like flagellae that enable them to swim short distances, ^[18]provided that at least a thin film of water is present. A shower of raindrops can help with their journey. In 2008, Japanese researchers found that some liverworts are able to fire sperm-containing water up to 15 cm into the air, allowing them to fertilize female plants growing more than a meter from the nearest male.

When sperm reach the archegonia, fertilization occurs, producing a diploid sporophyte. After fertilization, the immature sporophyte develops three distinct regions within the archegonium: (1) a leg , which both anchors the sporophyte in place and receives nutrients from its “mother” plant, (2) A spherical or ellipsoidal capsule , inside which are spores. Will be produced to spread to new locations, and (3) a seta (stalk) that lies between the other two regions and connects them. ^[18]When the sporophyte has developed all three regions, the seta elongate, force its way out of the archegonium and break it off. While the leg remains anchored within the parent plant, the capsule is ejected by the seta and extended away from the plant and into the air. Within the capsule, the cells divide to form both elator cells and spore-producing cells. The elaters are spring-like, and will open the capsule wall to scatter itself when the capsule bursts. Spore-producing cells undergo meiosis and spread to form haploid spores, at which point the life cycle can begin again.

Asexual reproduction

Some liverworts are capable of asexual reproduction; In bryophytes in general “it would be almost correct to say that vegetative reproduction is the rule and not the exception.” ^[20] For example, in Riccia , when the old parts of the spiny thalli die, the young tips become distinct individuals. ^[20]

Some thallose liverworts such as Marchantia polymorpha and Lunularia cruciata produce small disc-shaped gemme in shallow cups. ^[21]Marchantia gemmae can be spread up to 120 cm by splashing rain in the cup. ^[22] In Metzgeria , the gemmae thallus grows marginally. ^[23]Marchantia polymorpha is a common weed in greenhouses, often covering the entire surface of containers; ^[24] : 230 Gemma dispersal is “the primary mechanism by which liverwort spreads in a nursery or greenhouse.”

ecology

Today, liverworts can be found in many ecosystems across the planet, except in oceans and extremely dry environments, or those exposed to high levels of direct solar radiation. ^[25] As with most groups of living plants, they are most common (both in number and species) in moist tropical regions. ^[26] Liverworts are typically found in medium to deep shade, although desert species can tolerate direct sunlight and periods of total drying.

classification

relationship to other plants

Traditionally, liverworts were grouped with other bryophytes (mosses and hornworts) in the division Bryophyta, within which liverworts made up the class Hepatica ( also known as Marchantiopsida ). ^[8] [27] However, since this group makes the Bryophyta paraphyletic, liverworts are now usually given their own division. ^[28] The division name Bryophyta sensu lato is still used in the literature, but more often the name is used in a restricted sense to include only mosses.

Two hypotheses on the phylogeny of land plants (embryophyta). ^{[ citation needed ]}

Another reason that liverworts are now classified separately is that they have separated from all other embryonic plants near the beginning of their development. 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 genera. ^[29] The earliest addition fossils believed to be liverworts are compression fossils of Pallaviciniites from the Upper Devonian of New York. ^[30] These fossils resemble modern species of Metzgeriales. ^[31] Another Devonian fossil called Protosalvinia is also a liverwort .but its relation to other plants is still uncertain, so it may not belong to the Merchantiophyta. In 2007, the oldest fossils assigned to liverworts at that time were announced, Metzgeriothelus sharonae from the Givetian (Middle Devonian) of New York, United States. ^[32] However, in 2010, five different types of fossil liverwort spores were found in Argentina, dating to the middle Ordovician, about 470 million years ago. ^[1]^[33]

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 . ^[34] In addition to this taxon-based name, liverworts are often referred to as Hepaticophyta . The name is derived from their common Latin name because Latin was the language in which botanists published their descriptions of the species. The name has caused some confusion, ^[^{citation needed}^] partly because it appears to be a taxon-based name belonging to the genus Hepatica .Which is actually a flowering plant of the buttercup family Ranunculaceae. Furthermore, the name Hepaticophyta is often misspelled in textbooks as Hepatophyta , which only adds to the confusion.

Although there is no consensus among brologists regarding the classification of liverworts above the rank of the family, ^[35] the Marchantiophyta can be divided into three classes: ^[36]^[37]^{[38] [39}^]

Jungermanniopsida includes two orders Metzgeriales (simple thalloids) and Jungermanniales (leafy liverworts).
The Marchantiopsida includes the three orders Marchantiales (complex-thallus liverworts), and Sphaerocarpales (bottle hepatis), as well as Blasiales (previously placed among the Metzgeriales). ^[36] [40] It also includes the problematic genus Monoclea , which is sometimes placed in its own order. ^[41]
A third category, Haplomitriopsida , is recognized as a sister group to other liverworts ; ^[39] This includes the genera Haplomitrium , Trubia , and Apotreubia .

The diagram on the right summarizes a portion of a 2006 cladistic analysis of liverworts based on three chloroplast genes, one nuclear gene and one mitochondrial gene.

An updated classification by Soderstrom et al. 2016 ^[42]

Marchantiophyta Stotler and Krendel-Stotler 2000
- Haplomitriopsida Stotler और Crandall-Stotler 1977
  - Haplomitriels Hamlin 1972
  - Trebiels Shlajakov 1972
- Merchantiopsida Cronquist, Takhtjan and Zimmermann 1966
  - Blasiidae He-Nygrén 2006
    - Blasiales Stotler और Crandall-Stotler 2000
  - Marchantiidae Engler 1893 sensu He-Nygrén et al. 2006
    - Neohodgsoniles Long 2006
    - Sphaerocarpales Cavers 1910 (bottle liverworts )
    - lunularials long 2006
    - Marchantiales Limpricht 1877 (जटिल thalloids)
- Jungermaniopsida Stotler and Crandall-Stottler 1977
  - Pelidae Hay-Nigren et al. 2006
    - Peliales Hay-Nigren et al. 2006
    - Pallaviciniales Frey and Stech 2005
    - Fossombroniales Schljakov 1972
  - Metzgeridae Bartholomew-Began 1990
    - Plurozials Shljakov 1972
    - Metzgeriales Chalaud 1930
  - Jungermanidae angler 1893 (leafy liverworts)
    - Poreless Shlajakov 1972
    - Pitilidiales Shljakov 1972
    - Jungermanniels von Klinggraf 1858

It is estimated that there are about 9000 species of liverworts, of which at least 85% belong to the leafy group. ^[3] [43] Despite this fact, no liverwort genome has been sequenced to date and only a few genes have been identified and characterized.

economic importance

In ancient times, liverworts were believed to cure liver diseases, hence the name. ^[45] In Old English, the word liverwort literally means liver plant . ^[46] This probably stemmed from the superficial appearance of some thalloid liverworts, which in morphology resembled a liver, and took the group’s common name as hepatic , from the Latin word hepaticus for “pertaining to the liver” . An unrelated flowering plant, hepatica , is sometimes called liverwort because it was also used in the treatment of liver diseases. This archaic relationship of plant form to function was based on the “principle of signature”. ^[47]

Liverworts have little direct economic importance today. Their greatest impact is indirect through the reduction of erosion along river banks, their collection and water retention in tropical forests, and the formation of soil crust in deserts and polar regions. However, some species are directly used by humans. Some species, such as Riccia fluiton , are aquatic thallose liverworts that are sold for use in aquariums. Their thin, slender branches float on the surface of the water and provide habitat for both small invertebrates and the fish that feed on them.