Haplomitriopsida is a newly recognized

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

liverworts The Marchantiophyta () 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 ...

comprising fifteen species in three

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

. Recent

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analyses of

nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space *Nuclear ...

mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

l, and

plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosymbiotic cyan ...

gene sequences place this

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

group as the basal sister group to all other liverworts. The group thus provides a unique insight into the early

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

of liverworts in particular and of

land plants The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as siste ...

in general.

Description

Plants of '' Treubia'' grow as a prostrate leafy

thallus Thallus (plural: 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. Many of these organisms ...

. The

bifid Bifid refers to something that is split or cleft into two parts. It may refer to: * Bifid, a variation in the P wave, R wave, or T wave in an echocardiogram in which a wave which usually has a single peak instead has two separate peaks * Bifid ci ...

leaves extend like wings on either side of the midrib, or may be folded upwards and pressed close together, giving the plants a ruffled appearance. By contrast, ''

Haplomitrium ''Haplomitrium'' is a genus of liverwort The Marchantiophyta () 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 cel ...

'' grows as a subterranean

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow ...

with erect leafy stems. The thin, rounded leaves are arranged around the upright stems, giving the appearance of a soft moss. The species ''

Haplomitrium ovalifolium ''Haplomitrium'' is a genus of liverwort The Marchantiophyta () 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 cel ...

'' of

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

often has bifid leaves that are

asymmetrical Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...

, somewhat like those in ''Treubia''. ''Haplomitrium'' has a number of unique characters that distinguish it from other liverworts, such as lacking rhizoids. The vegetative stems possess a central

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

-conducting strand with large perforations derived from

plasmodesmata Plasmodesmata (singular: plasmodesma) are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Plasmodesmata evolved independently in several lineages, and spec ...

. This central strand is surrounded by a cylinder of cells that conduct food throughout the plant. Such an arrangement is evocative of the xylem and phloem found in

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

s. Although some thalloid liverwort species in the

Pallaviciniaceae Pallaviciniaceae is a widely distributed family of liverworts in the order Pallaviciniales. All species are thallose, typically organized as a thick central costa (midvein), each side with a broad wing of tissue one cell in thickness. All spec ...

also possess a central conducting strand, ''Haplomitrium'' differs in having a food-conducting layer and in producing no

callose Callose is a plant polysaccharide. Its production is due to the glucan synthase-like gene (GLS) in various places within a plant. It is produced to act as a temporary cell wall in response to stimuli such as stress or damage. Callose is composed ...

. ''Treubia'' also has features that differ from those found in other bryophytes, such as the differentiation of five identifiable zones in the stem midrib. Unlike other leafy species, the oil bodies in its

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

are restricted to certain clusters of cells, as they are in the

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. Phylogeny Based on the w ...

. These oil body clusters appear as dark spots in the leaves when the plant is held up to the light.

Diversity

Living representatives of the group exhibit an essentially

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

n distribution with its center of

diversity Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce *Diversity marketing, marketing communication targeting diverse customers * ...

Australasia Australasia is a region that comprises Australia, New Zealand and some neighbouring islands in the Pacific Ocean. The term is used in a number of different contexts, including geopolitically, physiogeographically, philologically, and ecologic ...

. Such a distribution implies that the modern genera radiated prior to the beginning of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

when Gondwana broke apart. Schuster proposes that species distributed in the northern hemisphere "rafted" on the

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...

subcontinent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

, then spread across the Bering Strait into

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

.Schuster, Rudolf M. (1983). "Phytogeography of the Bryophyta". Pages 463-626 ''in'' R. M. Schuster (ed.), ''New Manual of Bryology'' (Japan: Hattori Botanical Laboratory). . Most species in the Haplomitriopsida are found in south of the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...

, though there are northern ones. The genus '' Treubia'' is restricted to the southern hemisphere, while ''

Apotreubia ''Apotreubia'' is a genus of liverworts in the family Treubiaceae. There are four species, including: '' Apotreubia nana'', which is found in subalpine New Guinea, and '' Apotreubia pusilla'', which has a disjunct distribution between eastern As ...

'' has one species in

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torres ...

and another disjunct between eastern

and

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...

. The genus ''

'' exhibits a wider distribution, with species in both

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

, northern and central

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

, the

Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...

, and

Classification

Class Haplomitriopsida includes two

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

, each with one

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

. The group as a whole comprises fifteen

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

in three

. A fourth genus, '' Gessella'', is known only from

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...

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 preserved ...

s. The orders, families, and genera are as follows: * Subclass Haplomitriidae Stotler & Crand.-Stotl. ** Order

Calobryales Calobryales (formerly Haplomitriales) is an order of plants known as liverworts. This order contains one family, Haplomitriaceae, with a single extant genus ''Haplomitrium''. Taxonomy * Order Haplomitriales Buch ex Schljakov 1972 alobryales ...

Campbell ex Hamlin 1972 aplomitriales Buch ex Schljakov 1972*** Family

Haplomitriaceae Calobryales (formerly Haplomitriales) is an order of plants known as liverworts. This order contains one family, Haplomitriaceae, with a single extant genus ''Haplomitrium''. Taxonomy * Order Haplomitriales Buch ex Schljakov 1972 alobryales ...

Dědeček 1884 ****†'' Gessella'' Poulsen 1974 ****''

'' Nees 1833 nom. cons. (8 species) * Subclass Treubiidae Stotler & Crand.-Stotl. ** Order

Treubiales Treubiaceae is a family of liverworts in the order Treubiales.Crandall-Stotler, Barbara. & Stotler, Raymond E. "Morphology and classification of the Marchantiophyta". page 63 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology ...

Schljakov 1972 *** Family Treubiaceae Verdoorn 1932 ****''

'' Hattori & Mizutani 1966 (2 species) ****'' Treubia'' Goebel 1890 nom. cons. non Pierre 1890 (6 species) An additional fossil '' Treubiites kidstonii'' previously has been compared to the extant genus '' Treubia''. However, upon re-examination of the material, specimens were determined to be more like '' Blasia'' and not at all to resemble ''Treubia'' as previously thought. Accordingly, ''Treubiites'' is now assigned to the Blasiales rather than the Haplomitriopsida.

References

External links

Liverwort Tree of Life

{{Taxonbar, from=Q1051622 Liverworts Plant classes