Marchantiophyta

The Marchantiophyta /mɑːrˌkæntiˈɒfɪtə/ (listen) are a division of non-vascular land plants commonly referred to as hepatics or liverworts. 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.

It is estimated that there are about 9000 species of liverworts. Some of the more familiar species grow as a flattened leafless thallus, but most species are leafy with a form very much like a flattened moss. Leafy species can be distinguished from the apparently similar mosses on the basis of a number of features, including their single-celled rhizoids. Leafy liverworts also differ from most (but not all) mosses in that their leaves never have a costa (present in many mosses) and may bear marginal cilia (very rare in mosses). Other differences are not universal for all mosses and liverworts, but the occurrence of leaves arranged in three ranks, the presence of deep lobes or segmented leaves, or a lack of clearly differentiated stem and leaves all point to the plant being a liverwort.

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

Liverworts
Temporal range: 472–0 Ma
Mid-Ordovician[1] to present
Haeckel Hepaticae
"Hepaticae" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification
Kingdom: Plantae
Clade: Embryophytes
Division: Marchantiophyta
Stotler & Stotl.-Crand., 1977[2] emend. 2000[3]
Classes and Orders

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,[5] so they are often overlooked. The most familiar liverworts consist of a prostrate, flattened, ribbon-like or branching structure called a thallus (plant body); these liverworts are termed thallose liverworts. However, most liverworts produce flattened stems with overlapping scales or leaves in two or more ranks, the middle rank is often conspicuously different from the outer ranks; these are called leafy liverworts or scale liverworts.[6][7] (See the gallery below for examples.)

Lunularia cruciata
A thallose liverwort, Lunularia cruciata

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

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

Life cycle

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

Liverwort species may be either dioicous or monoicous. In 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.[16] 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 flagellae that enable them to swim short distances,[17] 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.[18]

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.[17] When the sporophyte has developed all three regions, the seta elongates, pushing its way out of the archegonium and rupturing it. While the foot remains anchored within the parent plant, the capsule is forced out by the seta and is extended away from the plant and into the air. Within the capsule, cells divide to produce both elater cells and spore-producing cells. The elaters are spring-like, and will push open the wall of the capsule to scatter themselves when the capsule bursts. The spore-producing cells will undergo meiosis to form haploid spores to disperse, upon which point the life cycle can start again.

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."[19] For example, in Riccia, when the older parts of the forked thalli die, the younger tips become separate individuals.[19]

Some thallose liverworts such as Marchantia polymorpha and Lunularia cruciata produce small disc-shaped gemmae in shallow cups.[20] Marchantia gemmae can be dispersed up to 120 cm by rain splashing into the cups.[21] In Metzgeria, gemmae grow at thallus margins.[22] Marchantia polymorpha is a common weed in greenhouses, often covering the entire surface of containers;[23]:230 gemma dispersal is the "primary mechanism by which liverwort spreads throughout a nursery or greenhouse."[23]:231

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.[24] As with most groups of living plants, they are most common (both in numbers and species) in moist tropical areas.[25] 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).[7][26] However, since this grouping makes the Bryophyta paraphyletic, the liverworts are now usually given their own division.[27] The use of the division name Bryophyta sensu lato is still found in the literature, but more frequently the Bryophyta now is used in a restricted sense to include only the mosses.

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

Another reason that liverworts are now classified separately is that they appear to have diverged from all other embryophyte plants near the beginning of their evolution. The strongest line of supporting evidence is that liverworts are the only living group of land plants that do not have stomata on the sporophyte generation.[28] Among the earliest fossils believed to be liverworts are compression fossils of Pallaviciniites from the Upper Devonian of New York.[29] These fossils resemble modern species in the Metzgeriales.[30] 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.[31] 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][32]

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

Although there is no consensus among bryologists as to the classification of liverworts above family rank,[34] the Marchantiophyta may be subdivided into three classes:[35][36][37][38]

The diagram at right summarizes a portion of a 2006 cladistic analysis of liverworts based upon three chloroplast genes, one nuclear gene, and one mitochondrial gene.[35]

Marchantiophyta
Haplomitriopsida

Haplomitriales

Treubiales

Marchantiopsida

Blasiales

Sphaerocarpales

Marchantiales

Jungermanniopsida

Metzgeriales (part)

Jungermanniales

Metzgeriales (part)

An updated classification by Söderström et al. 2016[41]

It is estimated that there are about 9000 species of liverworts, at least 85% of which belong to the leafy group.[3][42] Despite that fact, no liverwort genomes have been sequenced to date and only few genes identified and characterized.[43]

Economic importance

In ancient times, it was believed that liverworts cured diseases of the liver, hence the name.[44] In Old English, the word liverwort literally means liver plant.[45] 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".[46]

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:

Marchantia
Marchantia polymorpha, with antheridial and archegonial stalks.
Archegonium
The archegonium of Porella.
Porella SPT
A sporophyte of Porella emerging from its archegonium.
Porella platyphylla
Porella platyphylla clump growing on a tree.
Pellia epiphylla5 ies
Pellia epiphylla, growing on moist soil.
Plagiochila aspleniodes0
Plagiochila asplenioides, a leafy liverwort.
Liverwort
Conocephalum conicum, a large thallose liverwort.

See also

References

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  3. ^ a b Crandall-Stotler, Barbara; Stotler, Raymond E. (2000). "Morphology and classification of the Marchantiophyta". In A. Jonathan Shaw & Bernard Goffinet (Eds.) (eds.). Bryophyte Biology. Cambridge: Cambridge University Press. p. 21. ISBN 0-521-66097-1.CS1 maint: Uses editors parameter (link)
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External links

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.

Calycularia

Calycularia is the only genus of liverwort in the family Calyculariaceae. It was formerly included within the Allisoniaceae, and it includes only two species.

Cephaloziaceae

Cephaloziaceae is a family of liverworts.

Liverworts of this family are dioecious plants which have creeping or upright forms. They are green, brown, reddish, or purplish in color. The leaves are alternately arranged and succubous. Oil bodies are rare. They reproduce sexually, or vegetatively via gemmae.There are about 13 to 16 genera in this family.

They include:

Alobiella

Alobiellopsis

Anomoclada

Cephalozia

Cladopodiella

Fuscocephaloziopsis

Haesselia

Hygrobiella

Iwatsukia

Metahygrobiella

Nowellia

Odontoschisma

Pleurocladula

Schiffneria

Schofieldia

TrabacellulaFamily Cephaloziaceae is frequently rearranged. For example, genetic analysis suggests that genus Hygrobiella should be moved out of the family, and perhaps classified in a family of its own, and microscopic analysis of the morphology of Trabacellula also suggests it should be separated and made into a new family.

Division (biology)

Division is a taxonomic rank in biological classification that is used differently in zoology and in botany.

In botany and mycology, division refers to a rank equivalent to phylum. The use of either term is allowed under the International Code of Botanical Nomenclature, and both are commonly used in scientific literature.

The main Divisions of land plants, in the order in which they probably evolved, are the Marchantiophyta (liverworts), Anthocerotophyta (hornworts), Bryophyta (mosses), Filicophyta (ferns), Sphenophyta (horsetails), Cycadophyta (cycads), Ginkgophyta (ginkgo)s, Pinophyta (conifers), Gnetophyta (gnetophytes), and the Magnoliophyta (Angiosperms, flowering plants). The flowering plants now dominate terrestrial ecosystems, comprising 80% of vascular plant species.

In zoology, the term division is applied to an optional rank subordinate to the infraclass and superordinate to the cohort. A widely used classification (e.g. Carroll 1988) recognises teleost fishes as a Division Teleostei within Class Actinopterygii (the ray-finned fishes). Less commonly (as in Milner 1988), living tetrapods are ranked as Divisions Amphibia and Amniota within the clade of vertebrates with fleshy limbs (Sarcopterygii).

Ecological thinning

Ecological thinning is a silvicultural technique used in forest management that involves cutting trees to improve functions of a forest other than timber production.

Although thinning originated as a man-made forest management tool, aimed at increasing timber yields, the shift from production forests to multifunctional forests brought with it the cutting of trees to manipulate an ecosystem for various reasons, ranging from removing non-native species from a plot to removing poplars growing on a riverside beach aimed at recreational use.

Since the 1970s, leaving the thinned trees on the forest floor has become an increasingly common policy: wood can be decomposed in a more natural fashion, playing an important role in increasing biodiversity by providing habitat to various invertebrates, birds and small mammals. Many fungi (e.g. Calocera viscosa) and mosses are saproxylic or epixylic as well (e.g. Marchantiophyta) – some moss species completing their entire life-cycle on a single log.

Where trees are managed under a commercial regime, competition is reduced by removing adjacent stems that exhibit less favourable timber quality potential. When left in a natural state trees will "self-thin", but this process can be unreliable in some circumstances. Examples of this can be found in the Buxus – Ironbark forests and woodlands of Victoria (Australia) where a large proportion of trees are coppice, resultant from timber cutting in decades gone by.

Haplomitriopsida

Haplomitriopsida is a newly recognized class of liverworts comprising fifteen species in three genera. Recent cladistic analyses of nuclear, mitochondrial, and plastid gene sequences place this monophyletic group as the basal sister group to all other liverworts. The group thus provides a unique insight into the early evolution of liverworts in particular and of land plants in general.

Jungermanniopsida

Jungermanniopsida is the largest of three classes within the division Marchantiophyta (liverworts).

List of plant orders

This article lists the orders of the Viridiplantae.

Marchantiaceae

Marchantiaceae is a family of liverworts in order Marchantiales. It contains a single genus Marchantia.

Marchantiales

Marchantiales is an order of thallose liverworts that includes species like Marchantia polymorpha, a widespread plant often found beside rivers, and Lunularia cruciata, a common and often troublesome weed in moist, temperate gardens and greenhouses.

As in other bryophytes, the gametophyte generation is dominant, with the sporophyte existing as a short-lived part of the life cycle, dependent upon the gametophyte.

The genus Marchantia is often used to typify the order, although there are also many species of Asterella and species of the genus Riccia are more numerous.

The majority of genera are characterized by the presence of (a) special stalked vertical branches called archegoniophores or carocephala, and (b) sterile cells celled elaters inside the sporangium.

Marchantiopsida

Marchantiopsida is one of three classes within the liverwort phylum Marchantiophyta.

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 undifferentiated. All species in the order have a small gametophyte stage and a smaller, relatively short-lived, spore-bearing stage. Although these plants are almost entirely restricted to regions with high humidity or readily available moisture, the group as a whole is widely distributed, and occurs on every continent except Antarctica.

Neotrichocoleaceae

Neotrichocoleaceae is a family of liverworts in order Jungermanniales. It is closely related to the genera Ptilidium and Herzogianthus.

Non-vascular plant

Non-vascular plants are plants without a vascular system consisting of xylem and phloem. Although non-vascular plants lack these particular tissues, many possess simpler tissues that are specialized for internal transport of water.

Non-vascular plants include two distantly related groups:

Bryophytes, an informal group that is now treated as three separate land plant Divisions, namely Bryophyta (mosses), Marchantiophyta (liverworts), and Anthocerotophyta (hornworts). In all bryophytes, the primary plants are the haploid gametophytes, with the only diploid portion being the attached sporophyte, consisting of a stalk and sporangium. Because these plants lack lignified water-conducting tissues, they can't become as tall as most vascular plants.

Algae - especially the green algae. Recent studies have demonstrated that the algae consist of several unrelated groups. It turns out that the common features of living in water and photosynthesis were misleading as indicators of close relationship. Only those groups of algae included in the Viridiplantae are still considered relatives of land plants.These groups are sometimes referred to as "lower plants", referring to their status as the earliest plant groups to evolve, but the usage is imprecise, since both groups are polyphyletic and may be used to include vascular cryptogams, such as the ferns and fern allies that reproduce using spores. Non-vascular plants are often among the first species to move into new and inhospitable territories, along with prokaryotes and protists, and thus function as pioneer species.

Non-vascular plants do not have a wide variety of specialized tissue types. Mosses and leafy liverworts have structures called phyllids that look like leaves, but are not true leaves because they are single sheets of cells with no internal air spaces, no cuticle or stomata and no xylem or phloem. Consequently, phyllids are unable to control the rate of water loss from their tissues and are said to be poikilohydric. Some liverworts, such as Marchantia have a cuticle and the sporophytes of mosses have both cuticles and stomata, which were important in the evolution of land plants.All land plants have a life cycle with an alternation of generations between a diploid sporophyte and a haploid gametophyte, but in all non-vascular land plants the gametophyte generation is dominant. In these plants, the sporophytes grow from and are dependent on gametophytes for taking in water and mineral nutrients and for provision of photosynthate, the products of photosynthesis.

Perianth

The perianth (perigonium, perigon or perigone) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals). The term perianth is derived from the Greek περί, peri, meaning around, and άνθος, anthos, meaning flower, while perigonium is derived from gonos, meaning seed, i.e. sexual organs.

In the mosses and liverworts (Marchantiophyta), the perianth is the sterile tubelike tissue that surrounds the female reproductive structure (or developing sporophyte).

Rovno amber

Rovno amber, occasionally called Ukrainian amber, is amber found in the Rivne Oblast and surrounding regions of Ukraine and Belarus. The amber is dated between Late Eocene and Early Miocene, and suggested to be contemporaneous to Baltic amber. Major exploration and mining of the amber did not start until the 1990s.

Solenostomataceae

Solenostomataceae is a family of liverworts in order Jungermanniales.

Stomatophyta

The Stomatophyta are a proposed sister branch of the Marchantiophyta (Liverworts), together forming the Embryophyta. The Stomatophyta consist of the Bryophyta (Moss), and the remainder of the Embryophyta, including the Anthocerotophyta (Hornsworts). The word stomatophyta means plant with stoma.

An updated phylogeny of Embryophyta based on the work by Novíkov & Barabaš-Krasni 2015 with plant taxon authors from Anderson, Anderson & Cleal 2007 and some clade names from Pelletier 2012 and Lecointre, et al.

Treubiaceae

Treubiaceae is a family of liverworts in the order Treubiales. Species are large and leafy, and were previously classified among the Metzgeriales.

Rhodophyta
(red algae)
Glaucocystophyta
(glaucophytes)
Viridiplantae
(green algae,
& land plants)
Classification of Marchantiophyta
Haplomitriopsida
Jungermanniopsida
Marchantiopsida
Extant Life phyla/divisions by domain

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