Metzgeriales
Encyclopedia
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.
There is considerable diversity in vegetative structure of the Metzgeriales. As a rule, simple thalloid liverworts do not have structures resembling leaves. However, a few genera, such as Fossombronia, and Symphyogyna, are "semileafy" and have a thallus that is very deeply lobed, thus giving the appearance of leafiness. The genus Phyllothallia
has a more striking leafiness, with paired lobes of tissue spaced regularly at swollen nodes along a central, forked stem. The several semileafy groups within the Metzgeriales are not closely related to each other, and the currently accepted view is that the leafy condition evolved separately and independently in each of the groups where it occurs.
Members of the Metzgeriales also differ from the related Jungermanniales
in the location of their archegonia
(female reproductive structures). Whereas archegonia in the Jungermanniales develop directly from the apical cell at the tip of a fertile branch, archegonia in the Metzgeriales develop from a cell that is behind the apical cell. As a result, the female reproductive organs, and the sporophytes that develop within them, are always located on the dorsal surface of the plant. Because these structures do not develop at the apex of the branch, their development in the Metzgeriales is described as anacrogynous, from Greek
ἀν- (an-, "not") + ἄκρος (akros, "tip") + γυνή (gynē, “female”). The group was accordingly known as the Anacrogynae prior to being recognized as a separate order.
One simple thalloid liverwort is not photosynthetic. The species Cryptothallus mirabilis
is white as a result of lacking chlorophyll
, and has plastid
s that do not differentiate into chloroplast
s. This species is a myco-heterotroph
that obtains its nutrients from fungi
growing among its tissues. These plants grow in bogs and are typically found under peat moss
near birch
trees.
, although this relied heavily upon the prior work of Micheli (1729) and Dillenius (1741). Linnaeus included all 25 known species of liverworts, together with mosses, algae, and fungi, within a single class Cryptogamia. Linnaeus' system was heavily revised by workers in the early nineteenth century, so that by the time Endlicher published his Enchiridion Botanicum in 1841, five orders of liverworts were defined, and the "Frondosae" were segregated as a group that is congruent with the modern concept of the Metzgeriales. Endlicher's "Frondosae" included five subgroups (Metzgerieae, Aneureae, Haplolaeneae, Diplomitrieae, and Codonieae) with no assigned taxonomic rank
, but these groups were termed Familien by Dědeček in 1886. The same five subgroups of "Frondosae", without significant change, were used in the Synopsis Hepaticarum of Gottsche, Lindenberg, and Nees.
A more thorough understanding of the Metzgeriales was not achieved until the morphological
and developmental work of Leitgeb in the late nineteenth century. Leitgeb was among the first to recognize and appreciate the significance of development and reproductive morphology as a guide to distinguishing liverwort groups. His careful examinations guided revisions made in the classification published from 1893 to 1895 by Schiffner in Engler
and Prantl
. Schiffner thus divided his "Jungermanniales" into two broad groups according to whether the archegonia were terminal on reproductive branches (Jungermanniales akrogynae) or sub-terminal (Jungermanniales anakrogynae). This latter group included what are now recognized as the Metzgeriales, Sphaerocarpales
, and Haplomitriales
.
The simple thalloids were not given ordinal status until 1930 by Chalaud. Although subsequent systems similarly treated the group as distinct, the name of the order was more often given as "Jungermanniales anacrogynae" (or similar), or the group was retained within the Jungermanniales as a suborder with either this name or the name "Metzgerineae". The highly influential and comprehensive 1966 classification found in Schuster's Hepaticae and Anthocerotae of North America firmly established the name "Metzgeriales" for the group, although he had used this name in his earlier works. Schuster revised his system in 1972 and again in 1984. The only change he made in the circumscription of the Metzgeriales was to remove the Treubiales in accordance with that change made in the classification of Schljakov.
Schljakov's 1972 classification had elevated several subordinal groups within the simple thalloids to the rank of order, and treated the Metzgeriales itself as a superorder "Metzgerianae", but Schuster's 1984 system rejected most of these changes. The classification of Crandall-Stotler and Stotler (2000) adopted several of Schljakov's orders, while revising their membership and grouping them within a subclass "Metzgeriidae". These changes reflected a morphological analysis of species that had been presented three years earlier. Although their system changed the rank and the Latin ending of the name, the composition was identical to the Metzgeriales of Schuster (1966), with only the addition of the Haplomitriales
to its membership. Subsequent studies incorporating DNA sequence analysis have removed the Haplomitriales
, Treubiales, and Blasiales
and place those taxa elsewhere. The remnant of the group, after the removal of these taxa, consists of their Metzgeriales (7 families), Fossombroniales (4 families), and the Phyllothalliaceae.
Families marked with an asterisk * were classified in the separate order Fossombroniales by Crandall-Stotler and Stotler, but this grouping is not supported by subsequent analysis using DNA sequences.
Two additional families were formerly included within the Metzgeriales, but since have been transferred to other classes of liverwort. The Blasiaceae
has been assigned its own order Blasiales
, and phylogenetic studies show that it is more closely related to the Marchantiales
than to members of the Metzgeriales. Likewise, the Treubiaceae
is now in its own order Treubiales, within the recently recognized class Haplomitriopsida
.
Writing in 1984, Rudolf M. Schuster questioned the correct authority for the ordinal name. He believed that Underwood had first used the term, but concluded that as neither Underwood nor Chalaud had provided a formal description, the order should be cited as "Metzgeriales Schust. emend. Schljak." He ascribed first use of the name with a description to his own 1953 work on the liverworts of Minnesota
. This work included a considerable description sufficient to distinguish the order from all others, but Schuster relied on the 1972 emendation by Schljakov to provide the Latin diagnosis required by the International Code of Botanical Nomenclature. Schuster reaffirmed his position on the authority for publication in 1992.
In the publication of their revised liverwort classification in 2000, Crandall-Stotler and Stotler agreed with Schuster as to the attribution of the name, although they restricted their circumscription of the order considerably. However, upon additional review of the Chalaud paper, they reversed their opinion. They concluded that Chalaud's diagnosis, although "terse", was nonetheless adequate to satisfy the requirements for publication of a botanical name
, and that the Codes requirement for a Latin diagnosis did not apply, since the Chalaud paper was published prior to 1 January 1935. Chalaud is therefore the correct authority in citing the name "Metzgeriales".
(leafy liverworts) are more closely related to the Aneuraceae
and Metzgeriaceae
than are other simple thalloid groups.
Because plants belonging to the Metgeriales lack hard tissues, and the plants often decay or die back, preservation of fossil
s is dependent upon rapid burial by flood
s or volcanic ash
. Bryophytes are considered "delicate" plants, and this characteristic is often cited as the reason for the apparently poor fossil record of the group. However, fossils of the Metzgeriales are distributed widely, both geographically and stratigraphically, and the fossils which have been found are often highly detailed and well-preserved.
The oldest fossil bryophyte
is a compression fossil
of Pallavicinites devonicus from Upper Devonian
rocks that has been confidently assigned to the Metzgeriales. Portions of the fossil that have been isolated for microscopic examination reveal an extraordinary degree of cellular detail. The plant consisted of a thin, ribbon-like, bifurcating thallus with a thicker central midrib. The plant is remarkably similar in structure to members of the extant liverwort family Pallaviciniaceae
, but no reproductive structures have been found. Additional species assigned to the genus Pallavicinites have been found in rocks dating from the Carboniferous to the Pleistocene
.
Another early fossil probably belonging to the Metzgeriales is the Carboniferous
fossil Thallites willsi, which has been compared to the modern genus Metzgeria
. However, it has been assigned to the form genus
Thallites, which is used for thalloid fossil plants and algae
of uncertain relationships. Most fossils belonging to the Metzgeriales are assigned to the genus Metzgeriites
, which was established for this purpose. Specimens from the Upper Carboniferous of Shropshire
, England, have been named Hepaticites metzgerioides, and (as the specific epithet indicates) these specimens strongly resemble the genus Metzgeria. However, they have been placed instead in the form genus Hepaticites, used for fossils believed to be liverworts but without confident affiliation with any extant order. This species is not restricted to British localities, but has also been found in the Karagandy Province of Kazakhstan
.
Mesozoic
fossils of Metzgeriites have also been found. Metzgeriites glebosus has been collected from Jurassic
strata of Greenland
. The type material, and so far only material collected, consists of a midrib with a thin lamina that is deeply and irregularly lobed. A Cretaceous
fossil from Portugal
has been named Metzgeriites infracretaceus. Like M. glebosus, it possesses a midrib and thin lamina, but unlike that taxon the lamina of M. infracretaceus is not lobed.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of liverworts
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
. 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
Cellular differentiation
In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...
. All species in the order have a small gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
stage and a smaller, relatively short-lived, spore-bearing
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
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.
Description
Members of the Metzgeriales typically are small and thin enough to be translucent, with most of the tissues only a single cell layer in thickness. Because these plants are thin and relatively undifferentiated, with little evidence of distinct tissues, the Metzgeriales are sometimes called the "simple thalloid liverworts".Phyllothallia
Phyllothallia is a small genus of liverworts of the Southern Hemisphere. It is classified in order Metzgeriales and is the only member of the family Phyllothalliaceae within that order. Unlike most members of the Metzgeriales, Phyllothallia has a leafy appearance...
has a more striking leafiness, with paired lobes of tissue spaced regularly at swollen nodes along a central, forked stem. The several semileafy groups within the Metzgeriales are not closely related to each other, and the currently accepted view is that the leafy condition evolved separately and independently in each of the groups where it occurs.
Members of the Metzgeriales also differ from the related Jungermanniales
Jungermanniales
Jungermanniales is the largest order of liverworts. They are distinctive among the liverworts for having thin leaf-like flaps on either side of the stem...
in the location of their archegonia
Archegonium
An archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
(female reproductive structures). Whereas archegonia in the Jungermanniales develop directly from the apical cell at the tip of a fertile branch, archegonia in the Metzgeriales develop from a cell that is behind the apical cell. As a result, the female reproductive organs, and the sporophytes that develop within them, are always located on the dorsal surface of the plant. Because these structures do not develop at the apex of the branch, their development in the Metzgeriales is described as anacrogynous, from Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
ἀν- (an-, "not") + ἄκρος (akros, "tip") + γυνή (gynē, “female”). The group was accordingly known as the Anacrogynae prior to being recognized as a separate order.
Distribution and ecology
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.One simple thalloid liverwort is not photosynthetic. The species Cryptothallus mirabilis
Cryptothallus mirabilis
Cryptothallus mirabilis is a species of liverworts in the family Aneuraceae, and was first described in 1933. Plants of this species are white as a result of lacking chlorophyll, and their plastids do not differentiate into chloroplasts...
is white as a result of lacking chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
, and has plastid
Plastid
Plastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell...
s that do not differentiate into chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
s. This species is a myco-heterotroph
Myco-heterotrophy
Myco-heterotrophy is a symbiotic relationship between certain kinds of plants and fungi, in which the plant gets all or part of its food from parasitism upon fungi rather than from photosynthesis. A myco-heterotroph is the parasitic plant partner in this relationship...
that obtains its nutrients from fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
growing among its tissues. These plants grow in bogs and are typically found under peat moss
Sphagnum
Sphagnum is a genus of between 151 and 350 species of mosses commonly called peat moss, due to its prevalence in peat bogs and mires. A distinction is made between sphagnum moss, the live moss growing on top of a peat bog on one hand, and sphagnum peat moss or sphagnum peat on the other, the...
near birch
Birch
Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...
trees.
Classification
The beginning of modern liverwort nomenclature is marked with the 1753 publication of Linnaeus' Species PlantarumSpecies Plantarum
Species Plantarum was first published in 1753, as a two-volume work by Carl Linnaeus. Its prime importance is perhaps that it is the primary starting point of plant nomenclature as it exists today. This means that the first names to be considered validly published in botany are those that appear...
, although this relied heavily upon the prior work of Micheli (1729) and Dillenius (1741). Linnaeus included all 25 known species of liverworts, together with mosses, algae, and fungi, within a single class Cryptogamia. Linnaeus' system was heavily revised by workers in the early nineteenth century, so that by the time Endlicher published his Enchiridion Botanicum in 1841, five orders of liverworts were defined, and the "Frondosae" were segregated as a group that is congruent with the modern concept of the Metzgeriales. Endlicher's "Frondosae" included five subgroups (Metzgerieae, Aneureae, Haplolaeneae, Diplomitrieae, and Codonieae) with no assigned taxonomic rank
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
, but these groups were termed Familien by Dědeček in 1886. The same five subgroups of "Frondosae", without significant change, were used in the Synopsis Hepaticarum of Gottsche, Lindenberg, and Nees.
A more thorough understanding of the Metzgeriales was not achieved until the morphological
Plant morphology
Plant morphology or phytomorphology is the study of the physical form and external structure of plants. This is usually considered distinct from plant anatomy, which is the study of the internal structure of plants, especially at the microscopic level...
and developmental work of Leitgeb in the late nineteenth century. Leitgeb was among the first to recognize and appreciate the significance of development and reproductive morphology as a guide to distinguishing liverwort groups. His careful examinations guided revisions made in the classification published from 1893 to 1895 by Schiffner in Engler
Adolf Engler
Heinrich Gustav Adolf Engler was a German botanist. He is notable for his work on plant taxonomy and phytogeography, like Die Natürlichen Pflanzenfamilien , edited with Karl A. E...
and Prantl
Karl Anton Eugen Prantl
Karl Anton Eugen Prantl , also known as Carl Anton Eugen Prantl, was a German botanist.Prantl was born in Munich, Kingdom of Bavaria, and studied in Munich. In 1870 he graduated with the dissertation Das Inulin. Ein Beitrag zur Pflanzenphysiologie...
. Schiffner thus divided his "Jungermanniales" into two broad groups according to whether the archegonia were terminal on reproductive branches (Jungermanniales akrogynae) or sub-terminal (Jungermanniales anakrogynae). This latter group included what are now recognized as the Metzgeriales, Sphaerocarpales
Sphaerocarpales
Sphaerocarpales is an order of plants within the liverworts. Approximately twenty species are in this order which is sub-divided into three families: Sphaerocarpaceae and Riellaceae, as well as the extinct family Naiaditaceae...
, and Haplomitriales
Haplomitriales
Haplomitriales is an order of plants known as liverworts. The order is also called Calobryales in some sources, but the genus Calobryum is a synonym for Haplomitrium....
.
The simple thalloids were not given ordinal status until 1930 by Chalaud. Although subsequent systems similarly treated the group as distinct, the name of the order was more often given as "Jungermanniales anacrogynae" (or similar), or the group was retained within the Jungermanniales as a suborder with either this name or the name "Metzgerineae". The highly influential and comprehensive 1966 classification found in Schuster's Hepaticae and Anthocerotae of North America firmly established the name "Metzgeriales" for the group, although he had used this name in his earlier works. Schuster revised his system in 1972 and again in 1984. The only change he made in the circumscription of the Metzgeriales was to remove the Treubiales in accordance with that change made in the classification of Schljakov.
Schljakov's 1972 classification had elevated several subordinal groups within the simple thalloids to the rank of order, and treated the Metzgeriales itself as a superorder "Metzgerianae", but Schuster's 1984 system rejected most of these changes. The classification of Crandall-Stotler and Stotler (2000) adopted several of Schljakov's orders, while revising their membership and grouping them within a subclass "Metzgeriidae". These changes reflected a morphological analysis of species that had been presented three years earlier. Although their system changed the rank and the Latin ending of the name, the composition was identical to the Metzgeriales of Schuster (1966), with only the addition of the Haplomitriales
Haplomitriales
Haplomitriales is an order of plants known as liverworts. The order is also called Calobryales in some sources, but the genus Calobryum is a synonym for Haplomitrium....
to its membership. Subsequent studies incorporating DNA sequence analysis have removed the Haplomitriales
Haplomitriales
Haplomitriales is an order of plants known as liverworts. The order is also called Calobryales in some sources, but the genus Calobryum is a synonym for Haplomitrium....
, Treubiales, and Blasiales
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.- External links :* *...
and place those taxa elsewhere. The remnant of the group, after the removal of these taxa, consists of their Metzgeriales (7 families), Fossombroniales (4 families), and the Phyllothalliaceae.
Families
The Metzgeriales currently includes fourteen families, as follows:Families marked with an asterisk * were classified in the separate order Fossombroniales by Crandall-Stotler and Stotler, but this grouping is not supported by subsequent analysis using DNA sequences.
Two additional families were formerly included within the Metzgeriales, but since have been transferred to other classes of liverwort. The Blasiaceae
Blasiaceae
Blasiaceae is a family of liverworts with only two species: Blasia pusilla and Cavicularia densa . The family has traditionally been classified among the Metzgeriales, but molecular cladistics suggests a placement at the base of the Marchantiopsida.- External links :* *...
has been assigned its own order Blasiales
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.- External links :* *...
, and phylogenetic studies show that it is more closely related to the Marchantiales
Marchantiales
Marchantiales is an order of thallose liverworts that includes species like Lunularia cruciata, a common and often troublesome weed in moist, temperate gardens and greenhouses....
than to members of the Metzgeriales. Likewise, the Treubiaceae
Treubiaceae
Treubiaceae is a family of liverworts in the order Treubiales. Species are large and leafy, and were previously classified among the Metzgeriales....
is now in its own order Treubiales, within the recently recognized class Haplomitriopsida
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...
.
Botanical authority
In previous decades, there has been considerable confusion over the correct attribution of the name "Metzgeriales". The ordinal name Metzgeriales was first published by Chalaud in 1930 with the description “J’ai désigné très généralement les Jungermannniales anacrogynes sous le nom de Metzgériales,” (that is: "I have designated very generally the Jungermannniales anacrogynes under the name of Metzgeriales"). Chalaud cited Underwood 1894 in support of his treatment, but Underwood himself used only the name Metzgeriaceae for the group, and considered the whole to represent a single family. The publication of the ordinal name by Chalaud was accepted as correct by Grolle in his 1983 synopsis of the generic and higher-rank names of liverworts.Writing in 1984, Rudolf M. Schuster questioned the correct authority for the ordinal name. He believed that Underwood had first used the term, but concluded that as neither Underwood nor Chalaud had provided a formal description, the order should be cited as "Metzgeriales Schust. emend. Schljak." He ascribed first use of the name with a description to his own 1953 work on the liverworts of Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
. This work included a considerable description sufficient to distinguish the order from all others, but Schuster relied on the 1972 emendation by Schljakov to provide the Latin diagnosis required by the International Code of Botanical Nomenclature. Schuster reaffirmed his position on the authority for publication in 1992.
In the publication of their revised liverwort classification in 2000, Crandall-Stotler and Stotler agreed with Schuster as to the attribution of the name, although they restricted their circumscription of the order considerably. However, upon additional review of the Chalaud paper, they reversed their opinion. They concluded that Chalaud's diagnosis, although "terse", was nonetheless adequate to satisfy the requirements for publication of a botanical name
Botanical name
A botanical name is a formal scientific name conforming to the International Code of Botanical Nomenclature and, if it concerns a plant cultigen, the additional cultivar and/or Group epithets must conform to the International Code of Nomenclature for Cultivated Plants...
, and that the Codes requirement for a Latin diagnosis did not apply, since the Chalaud paper was published prior to 1 January 1935. Chalaud is therefore the correct authority in citing the name "Metzgeriales".
Phylogeny
The Metzgeriales are a paraphyletic group of liverworts, in that they do not include all the descendants of their most recent common ancestor. Specifically, the JungermannialesJungermanniales
Jungermanniales is the largest order of liverworts. They are distinctive among the liverworts for having thin leaf-like flaps on either side of the stem...
(leafy liverworts) are more closely related to the Aneuraceae
Aneuraceae
Aneuraceae is a family of thallose liverworts in the order Metzgeriales. Most species are very small with narrow, branching thalli....
and Metzgeriaceae
Metzgeriaceae
Metzgeriaceae is a family of thallose liverworts in the order Metzgeriales. Species may be either monoicous or dioicous....
than are other simple thalloid groups.
The diagram at right summarizes a portion of a 2006 cladistic analysis Cladistics Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade... of liverworts based upon three chloroplast genes, one nuclear gene, and one mitochondrial gene. The genus Sandeothallus Sandeothallus Sandeothallus is a small genus of liverworts restricted to East Asia. It is classified in order Metzgeriales and is the only member of the family Sandeothallaceae within that order.... and the species Mizutania riccardioides Mizutania Mizutania is a genus of liverworts restricted to tropical Asia, and contains a single species Mizutania riccardioides. It is classified in order Metzgeriales and is the only member of the family Mizutaniaceae within that order.... and Vandiemenia ratkowskiana Vandiemenia Vandiemenia ratkowskiana is the only species of liverwort in the genus Vandiemenia. It is endemic to Tasmania, Australia. Its natural habitat is subtropical or tropical dry forests.... (each the only member of its respective family) were not included in the study. Linked names at the tips of clade branches are families currently assigned to the Metzgeriales. Names which are not linked belong to other groups. The results agree with the view that the Metzgeriales are paraphyletic as a result of including neither the Jungermanniales Jungermanniales Jungermanniales is the largest order of liverworts. They are distinctive among the liverworts for having thin leaf-like flaps on either side of the stem... nor Pleuroziaceae (both shown in bold), which nest among the simple thalloid liverworts. |
Fossil record
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s is dependent upon rapid burial by flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
s or volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
. Bryophytes are considered "delicate" plants, and this characteristic is often cited as the reason for the apparently poor fossil record of the group. However, fossils of the Metzgeriales are distributed widely, both geographically and stratigraphically, and the fossils which have been found are often highly detailed and well-preserved.
The oldest fossil bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
is a compression fossil
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...
of Pallavicinites devonicus from Upper Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
rocks that has been confidently assigned to the Metzgeriales. Portions of the fossil that have been isolated for microscopic examination reveal an extraordinary degree of cellular detail. The plant consisted of a thin, ribbon-like, bifurcating thallus with a thicker central midrib. The plant is remarkably similar in structure to members of the extant liverwort family Pallaviciniaceae
Pallaviciniaceae
Pallaviciniaceae is a widely-distributed family of liverworts in the order Metzgeriales. All species are thallose, typically organized as a thick central costa , each side with a broad wing of tissue one cell in thickness. All species are dioicous...
, but no reproductive structures have been found. Additional species assigned to the genus Pallavicinites have been found in rocks dating from the Carboniferous to the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
.
Another early fossil probably belonging to the Metzgeriales is the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
fossil Thallites willsi, which has been compared to the modern genus Metzgeria
Metzgeria
Metzgeria is a genus of thalloid liverworts in the family Metzgeriaceae. The genus was named in honor of Johann Christian Metzger, former director of the Heidelberg Botanical Garden....
. However, it has been assigned to the form genus
Form taxon
Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships...
Thallites, which is used for thalloid fossil plants and algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
of uncertain relationships. Most fossils belonging to the Metzgeriales are assigned to the genus Metzgeriites
Metzgeriites
Metzgeriites is a genus of fossil liverwort....
, which was established for this purpose. Specimens from the Upper Carboniferous of Shropshire
Shropshire
Shropshire is a county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. It borders Wales to the west...
, England, have been named Hepaticites metzgerioides, and (as the specific epithet indicates) these specimens strongly resemble the genus Metzgeria. However, they have been placed instead in the form genus Hepaticites, used for fossils believed to be liverworts but without confident affiliation with any extant order. This species is not restricted to British localities, but has also been found in the Karagandy Province of Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
.
Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
fossils of Metzgeriites have also been found. Metzgeriites glebosus has been collected from Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
strata of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
. The type material, and so far only material collected, consists of a midrib with a thin lamina that is deeply and irregularly lobed. A Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
fossil from Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
has been named Metzgeriites infracretaceus. Like M. glebosus, it possesses a midrib and thin lamina, but unlike that taxon the lamina of M. infracretaceus is not lobed.
External links
- Metzgeriales photos from Finland
- University of Hawai'i at Mānoa : Metzgeriales information and images, part 1 and part 2