Haplomitriopsida is a

class Class, Classes, 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 d ...

liverworts Liverworts are a group of non-vascular plant, non-vascular embryophyte, land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in wh ...

comprising fifteen species in three

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

. Recent

cladistic Cladistics ( ; from Ancient Greek 'branch') 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 ...

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 us ...

l, and

plastid A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria. Examples of plastids include chloroplasts ...

gene sequences place this

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group as the basal

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

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

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

of liverworts in particular and of

land plants The embryophytes () are a clade of plants, also known as Embryophyta (Plantae ''sensu strictissimo'') () or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophy ...

in general.

Description

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

thallus Thallus (: 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. A thallus usually names the entir ...

. The bifid 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'' grows as a

subterranean Subterranean(s) or The Subterranean(s) may refer to: * Subterranea (geography), underground structures, both natural and man-made Literature * ''Subterranean'' (novel), a 1998 novel by James Rollins * ''Subterranean Magazine'', an American fa ...

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

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'' of Australia 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-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 spe ...

. 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 (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...

s. Although some thalloid liverwort species in the Pallaviciniaceae 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 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. Complex oil bodies are on ...

. 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, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

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 subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different context ...

. 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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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

subcontinent A continent is any of several large geographical regions. Continents are generally identified by convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as in the case of A ...

to Asia, then spread across the

Bering Strait The Bering Strait ( , ; ) is a strait between the Pacific and Arctic oceans, separating the Chukchi Peninsula of the Russian Far East from the Seward Peninsula of Alaska. The present Russia–United States maritime boundary is at 168° 58' ...

into North America.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, though there are northern ones. The genus '' Treubia'' is restricted to the southern hemisphere, while '' Apotreubia'' has one species in

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

and another disjunct between eastern

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

and

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

. The genus '' Haplomitrium'' exhibits a wider distribution, with species in both North and South America, northern and central Europe, the Himalayas, Japan, and Australasia.

Classification

The orders, families, and genera within class Haplomitriopsida 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 Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), aff ...

Hamlin *** Family Haplomitriaceae Dědeček ****†'' Gessella'' C.Poulsen ****'' Haplomitrium''

Nees Christian Gottfried Daniel Nees von Esenbeck (14 February 1776 – 16 March 1858) was a prolific German botanist, physician, zoologist, and natural philosopher. He was a contemporary of Goethe and was born within the lifetime of Linnaeus. ...

* Subclass Treubiidae Stotler & Crand.-Stotl. ** Order Treubiales Schljakov *** Family Treubiaceae Verd. ****'' Apotreubia'' S.Hatt. & Mizut. ****'' Treubia'' K.I.Goebel

References

External links

Liverwort Tree of Life

{{Taxonbar, from=Q1051622 Liverworts Plant classes