Marchantiophyta
Liverworts Mid- | |
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"Hepaticae" from Ernst Haeckel's Kunstformen der Natur, 1904 | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Embryophytes |
Clade: | Setaphyta |
Division: | Marchantiophyta Stotler & Stotl.-Crand., 1977[2] emend. 2000[3] |
Classes and orders | |
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The Marchantiophyta (
It is estimated that there are about 9000 species of liverworts.
Liverworts are typically small, usually from 2–20 mm (0.079–0.787 in) wide with individual plants less than 10 cm (3.9 in) 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.[5]
Physical characteristics
Description
Most liverworts are small, measuring from 2–20 millimetres (0.08–0.8 in) wide with individual plants less than 10 centimetres (4 in) long,[6] 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 leafy liverworts or scale liverworts.[7][8] (See the gallery below for examples.)
Liverworts can most reliably be distinguished from the apparently similar
Liverworts, like other bryophytes, have a
Life cycle
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.[16][17] 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).[8] Each archegonium has a slender hollow tube, the "neck", down which the sperm swim to reach the egg cell.
Liverwort species may be either
When sperm reach the archegonia,
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."[23] For example, in Riccia, when the older parts of the forked thalli die, the younger tips become separate individuals.[23]
Some thallose liverworts such as Marchantia polymorpha and Lunularia cruciata produce small disc-shaped gemmae in shallow cups.[24] Marchantia gemmae can be dispersed up to 120 cm by rain splashing into the cups.[25] In Metzgeria, gemmae grow at thallus margins.[26] Marchantia polymorpha is a common weed in greenhouses, often covering the entire surface of containers;[27]: 230 gemma dispersal is the "primary mechanism by which liverwort spreads throughout a nursery or greenhouse."[27]: 231
Symbiosis
Thalloid liverworts typically harbor symbiotic
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.[29] As with most groups of living plants, they are most common (both in numbers and species) in moist tropical areas.[30] 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).[8][31] Somewhat more recently, the liverworts were given their own division (Marchantiophyta),[32] as bryophytes became considered to be 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.[33][34][35][36][37][38][39][40][41][excessive citations] Hence, it has been suggested that the liverworts should be de-ranked to a class called Marchantiopsida.[35] In addition, there is strong phylogenetic evidence to suggest that liverworts and mosses form a monophyletic subclade named Setaphyta.[34][42][43]
'Monophyletic bryophytes' model | 'Liverworts plus mosses–basal' model | ||||||||||||||||||||||||||||||||||||||||||||
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Two of the most likely models for bryophyte evolution.[43] |
An important conclusion from these phylogenies is that the ancestral stomata appear to have been lost in the liverwort lineage.[34][38] Among the earliest fossils believed to be liverworts are compression fossils of Pallaviciniites from the Upper Devonian of New York.[44] These fossils resemble modern species in the Metzgeriales.[45] 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, United States.[46] 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.[1][47]
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.[48] 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,[citation needed] 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.
Although there is no consensus among bryologists as to the classification of liverworts above family rank,[49] the Marchantiophyta may be subdivided into three classes:[50][51][52][53]
- 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).[50][54] It also includes the problematic genus Monoclea, which is sometimes placed in its own order Monocleales.[55]
- A third class, the Haplomitriopsida is newly recognized as the sister group of the other liverworts;[53] it comprises the genera Haplomitrium, Treubia, and Apotreubia.
Forrest 2006[50] | Cole, Hilger & Goffinet 2021 [56] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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An updated classification by Söderström et al. 2016[57]
- Marchantiophyta Stotler & Crandall-Stotler 2000
- Haplomitriopsida Stotler & Crandall-Stotler 1977
- CalobryalesHamlin 1972
- TreubialesSchljakov 1972
- Marchantiopsida Cronquist, Takhtajan & Zimmermann 1966
- BlasiidaeHe-Nygrén et al. 2006
- Blasiales Stotler & Crandall-Stotler 2000
- MarchantiidaeEngler 1893 sensu He-Nygrén et al. 2006
- LunularialesLong 2006
- Marchantiales Limpricht 1877 (complex thalloids)
- NeohodgsonialesLong 2006
- Sphaerocarpales Cavers 1910 (bottle liverworts)
- Jungermanniopsida Stotler & Crandall-Stotler 1977
- JungermanniidaeEngler 1893 (leafy liverworts)
- Jungermanniales von Klinggräff 1858
- Porellales Schljakov 1972
- Ptilidiales Schljakov 1972
- Metzgeriidae Bartholomew-Began 1990
- Metzgeriales Chalaud 1930
- PleurozialesSchljakov 1972
- Pelliidae He-Nygrén et al. 2006
- Fossombroniales Schljakov 1972
- Pallaviciniales Frey & Stech 2005
- Pelliales He-Nygrén et al. 2006
- Haplomitriopsida Stotler & Crandall-Stotler 1977
It is estimated that there are about 9000 species of liverworts, at least 85% of which belong to the leafy group.[3][58] Despite that fact, no liverwort genomes have been sequenced to date and only few genes identified and characterized.[59]
Economic importance
In ancient times, it was believed that liverworts cured diseases of the liver, hence the name.[60] In Old English, the word liverwort literally means liver plant.[61] 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".[62]
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 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 aquariums. 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:
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Marchantia polymorpha, with antheridial and archegonial stalks.
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The archegonium of Porella.
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A sporophyte of Porella emerging from its archegonium.
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Porella platyphylla clump growing on a tree.
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Pellia epiphylla, growing on moist soil.
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Plagiochila asplenioides, a leafy liverwort.
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Riccia fluitans, an aquatic thallose liverwort.
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Conocephalum conicum, a large thallose liverwort.
See also
References
- ^ a b Walker, Matt. "Fossils of earliest land plants discovered in Argentina" [1]. (BBC, Earth News, 2010).
- JSTOR 3242017.
- ^ ISBN 0-521-66097-1.
- ^ Liverworts Homepage | UNB
- ISBN 0-914868-21-7.
- ^ Schuster, Rudolf M. The Hepaticae and Anthocerotae of North America, vol. I, pp. 243–244. (New York: Columbia University Press, 1966)
- ^ Kashyap, Shiv Ram. Liverworts of the Western Himalayas and the Panjab Plain, vol. I, p. 1. (New Delhi: The Chronica Botanica, 1929)
- ^ ISBN 0-02-949660-8.
- ISBN 49381633045.
- ^ Allison, K. W. & John Child. The Liverworts of New Zealand, pp. 13–14. (Dunedin: University of Otago Press, 1975).
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- ^ Volume 1, Chapter 11-1: Photosynthesis: The Process
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- ^ a b Campbell, Douglas H. The Structure and Development of Mosses and Ferns, pp. 73–74. (London: The Macmillan Co., 1918)
- .
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- PMID 21652320.
- ^ a b Lepp, Heino (15 April 2008). "Vegetative Reproduction". Australian Bryophytes. Australian National Botanic Gardens. Retrieved 22 December 2011.
- ^ Smith, AJE (1989) The Liverworts of Britain and Ireland, Cambridge University Press, Cambridge.
- ^ Equihua, C. (1987). "Splash-Cup Dispersal Of Gemmae In The Liverwort Marchantia-Polymorpha". Cryptogamie, Bryologie, Lichénologie. 8 (3): 199–217. Archived from the original on 26 April 2012.
- ^ Lepp, Heino (28 February 2008). "Reproduction & Dispersal". Australian Bryophytes. Australian National Botanic Gardens. Retrieved 22 December 2011.
- ^ a b Newby, Adam; Altland, James E.; Gilliam, Charles H.; Wehtje, Glenn (December 2006). "Postemergence Liverwort Control in Container-Grown Nursery Crops1" (PDF). J. Environ. Hort. 24 (4). Horticultural Research Institute: 230–236. Archived from the original (PDF) on 24 July 2012. Retrieved 24 December 2011.
- PMID 19812075.
- ^ Schuster, Rudolf M. The Hepaticae and Anthocerotae of North America, vol. I, pp. 243–249. (New York: Columbia University Press, 1966).
- ISBN 0-412-22340-6.
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- ^ Heinrichs, Jochen; 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.
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- ^ Forrest, Laura L.; Barbara J. Crandall-Stotler (2004). "A Phylogeny of the Simple Thalloid Liverworts (Jungermanniopsida, Metzgeriidae) as Inferred from Five Chloroplast Genes". Monographs in Systematic Botany. Molecular Systematics of Bryophytes. 98. Missouri Botanical Garden Press: 119–140.
- ISBN 0-914868-21-7.
- ^ Cole, Theodor C. H.; Hilger, Hartmut H.; Goffinet, Bernard. "Bryophyte phylogeny poster: systematics and Characteristics of Nonvascular Land Plants (Mosses, Liverworts, Hornworts)". 2021. Retrieved 6 December 2022.
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- ^ Dittmer, Howard J. Phylogeny and Form in the Plant Kingdom, p. 286. (Toronto: D. Van Nostrand Co., 1964)
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External links
- Media related to Marchantiophyta at Wikimedia Commons
- Data related to Marchantiophyta at Wikispecies
- Liverwort structure in pictures
- LiToL: Assembling the Liverwort Tree of Life (note: for 500,000 million years ago read "480 million years ago".)
- Inter-relationships of Mosses, Liverworts, and Hornworts
- Additional information on Liverworts
- Liverworts