Porella Platyphylla
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''Porella platyphylla'' is a species of
liverwort Liverworts are a group of non-vascular 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 which cells of the plant carry ...
belonging to the family Porellaceae. It has a
Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical reg ...
distribution, occurring across
Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...
and North America, where it typically grows on tree bark and rocks in areas with adequate rainfall. The species is most common in regions receiving at least 600 millimetres of annual precipitation. The species forms part of a complex taxonomic group that includes several closely related species and hybrids, with populations showing distinct genetic differences between continents despite their morphological similarity. The species is characterised by its obtuse-rounded leaf lobes with flat margins, and irregular teeth at the
perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower. It is a structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals) or tepal ...
mouth when mature. It reproduces both sexually, with separate male and female plants, and asexually through leaf fragments. ''P. platyphylla'' is known for its ability to survive long periods of
desiccation Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. The ...
, being able to recover normal
photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...
function within hours of rehydration. The species produces unique chemical compounds, including pinguisane
sesquiterpenoid Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many combinations. Biochemical modifications such ...
s and sacculatane
diterpenoid Diterpenes are a class of terpenes composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate being a primar ...
s, which help distinguish it from related species. Recent
molecular A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...
studies have revealed significant
genetic variation Genetic variation is the difference in DNA among individuals or the differences between populations among the same species. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources ...
within the species, particularly in European populations, though this variation is not always reflected in physical characteristics.


Taxonomy

The species was first described by
Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...
, with early descriptions and illustrations provided by
Pier Antonio Micheli Pier Antonio Micheli (11 December 1679 – 1 January 1737) was a noted Italian botanist, professor of botany in Pisa, curator of the Orto Botanico di Firenze, author of ''Nova plantarum genera iuxta Tournefortii methodum disposita''. He discover ...
(1729) and
Johann Jacob Dillenius Johann Jacob Dillen Dillenius (1684 – 2 April 1747) was a German botanist. He is known for his ''Hortus Elthamensis'' ("Eltham Garden") on the rare plants around Eltham, London, and for his ''Historia muscorum'' ("History of Mosses"), a natu ...
(1741). ''P. platyphylloidea'' was later described by
Lewis David von Schweinitz Lewis David de Schweinitz (13 February 1780 – 8 February 1834) was a German-American botanist and mycologist from Bethlehem, Pennsylvania. Considered the "Father of North American Mycology," he also made significant contributions to botany. ...
in 1821 from a
North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...
collection, who distinguished it primarily by its occurrence on rocks rather than bark, larger plants with often branching, leaves with margins, and differences in the relative sizes of the plant's structural features. Historical taxonomic treatments varied in their interpretation of these plants. While some researchers like
Marshall Avery Howe Marshall Avery Howe (June 6, 1867 in Newfane, Vermont1000 Men
by Dorman Bridgman Eaton K ...
(1897) and
Theodore Christian Frye Theodore Christian Frye (September 15, 1869, Washington, Illinois – April 5, 1962, Seattle) was an American botany professor and one of the world's leading experts on bryology. Biography Born on a farm near Washington, Illinois, Theodore C. Frye ...
and Lois Clark (1946) treated them as a single variable species, others such as
Alexander William Evans Alexander William Evans (May 17, 1868 – December 6, 1959) was a botanist, bryologist, and mycologist that specialized in the flora of Connecticut. Early life Born in Buffalo, New York on May 17, 1868, Evan's family moved to New Haven, Connect ...
(1916), Karl Müller of Freiburg (1915), and Rudolf Mathias Schuster (1980) maintained them as separate species. The perianth mouth structure and elater spiral patterns were particularly emphasised as diagnostic features by later authors. A comprehensive 1998 study examining both morphological and genetic variation in ''Porella platyphylla'' and ''P. platyphylloidea'' led to a significant taxonomic revision. The research, which analysed 35 populations across North America and Europe, revealed three distinct genetic groups within what had previously been considered two separate species. To help stabilize the taxonomy of this complex group, researchers later designated a DNA voucher specimen from Germany (Heinrichs and Feldberg 4600) as an
epitype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
for ''P. platyphylla''.


Related species

''Porella platyphylla'' forms part of a complex of closely related taxa, with its closest relative being '' P. cordaeana''. DNA analyses have revealed two main
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
s within ''P. platyphylla'': one predominantly North American and another widespread in Europe but also present in North America and Asia. Both species maintain distinct European and North American lineages that form sister groups in
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
analyses. ''Porella cordaeana'' can be distinguished from ''P. platyphylla'' by its -
sinuous Sinuosity, sinuosity index, or sinuosity coefficient of a continuously differentiable curve having at least one inflection point is the ratio of the curvilinear length (along the curve) and the Euclidean distance ( straight line) between the ...
perianth mouth and acute, ventrally reflexed and twisted lobules. While both species have leaf lobules that fold under, in ''P. cordaeana'' these are twisted and taper to a point, whereas in ''P. platyphylla'' they are merely folded under without twisting and have rounded or obtuse tips. These species can sometimes be found growing together in the same habitat, and multiple species may even grow intermixed within a single
colony A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their ''metropole'' (or "mother country"). This separated rule was often orga ...
. This close physical association, combined with their ability to reproduce sexually, has led to hybridisation between species. A hybrid between these species, has been documented in Europe. This hybrid is an
allopolyploid Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...
, meaning it originated through hybridisation between two species and underwent chromosome doubling. While ''P. platyphylla'' and ''P. cordaeana'' are typically haploid with eight chromosomes (occasionally nine in ''P. platyphylla''), their hybrid derivative is polyploid. Genetic evidence suggests this hybridisation event was relatively recent, and the hybrid may have originated multiple times. Analyses of
chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
and
nuclear DNA Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. ...
have produced conflicting
evolutionary tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In o ...
s, suggesting that the North American populations formerly known as ''P. platyphylloidea'' may be the result of ancient hybridisation between ''P. cordaeana'' and ''P. platyphylla'', though through a different and much older hybridisation event than that which produced .


Description

''Porella platyphylla'' shows several distinctive morphological features that help identify it, though these can show considerable variation both within single populations and between different geographical regions. The leaves have tips (known as lobes) that are obtuse-rounded in shape, with edges that lie flat rather than being wavy or folded. The cells in the middle portion of these lobes measure between 28.5 and 36.1 
μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...
in width. A key identifying feature of the species is found in its
perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower. It is a structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals) or tepal ...
—a protective tube-like structure that surrounds the developing reproductive organs in female plants. When fully mature, the mouth of this perianth has irregularly spaced teeth that are 2–6 cells wide at their base. The female reproductive structures (called bracts) typically have smooth, unbroken edges, unlike some related species which may have toothed or spiny margins. Features previously used to distinguish ''P. platyphylla'' from ''P. platyphylloidea'', such as leaf lobule width and elater spiral patterns, have shown no consistent correlation with genetic groupings. Even populations that were genetically identical sometimes displayed different morphological characteristics traditionally used to separate the species. More recent
molecular A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...
studies have revealed the existence of
cryptic species In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
—genetically distinct lineages that cannot be reliably distinguished through morphological examination alone. While some tendencies exist, such as larger leaf lobules being more common in North American populations, these characteristics are not consistent enough for reliable identification. This challenge is further complicated by evidence that some populations may represent ancient hybrid lineages, explaining the high degree of morphological variability observed within populations and the unreliability of traditionally used diagnostic features.


Life history

The
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from conception to reproduction *Life-cycle hypothesis, in economics *Erikson's stages of psy ...
and development of ''Porella platyphylla'' was first studied in detail in the early 20th century. Like other liverworts, this species displays distinct stages in its life cycle, including both a dominant
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the se ...
(the main plant body) and a smaller
sporophyte A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...
phase.


Vegetative structure

The main plant body (gametophyte) grows flat against its
substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...
in a pattern known as (having distinct upper and lower surfaces). It develops from a pyramid-shaped growing tip called an apical cell, which continually divides to form new tissue. The plant produces three rows of leaves: two rows on the upper () surface and one row on the lower () surface. The ventral leaves, technically called amphigastria, are supplemented by special flaps or lobes from the dorsal leaves that fold underneath, giving the appearance of five rows of leaves when viewed from below.


Reproduction

''Porella platyphylla'' reproduces sexually, with male and female reproductive organs developing on short side branches. The female organs (
archegonia An archegonium (: archegonia), from the Ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamet ...
) develop on particularly short branches and consist of a protective jacket of cells surrounding a central channel containing an egg cell. The male organs (
antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. The androecium is al ...
) form on slightly longer branches and produce sperm cells. Each antheridium develops on a long, slender stalk made up of two rows of cells. Individual colonies are often multiclonal, with male and female plants growing intermixed, indicating establishment from multiple spores. While female plants are relatively common (about 49% of shoots), male plants are less frequently found (around 10% of shoots). After fertilisation, the
embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...
develops into a sporophyte—the spore-producing generation. The mature sporophyte consists of a capsule containing spores mixed with elongated cells called
elater An elater is a cell (or structure attached to a cell) that is hygroscopic, and therefore will change shape in response to changes in moisture in the environment. Elaters come in a variety of forms, but are always associated with plant spores. In ...
s, which help disperse the spores. The sporophyte base forms a foot that anchors it to the parent plant, with the shape of this foot varying from club-like to anchor-shaped.


Survival adaptations

One main characteristic of ''P. platyphylla'' is its ability to survive long periods of drying out (desiccation). The plant can remain dormant in a dried state for months or even years, reviving quickly when moisture becomes available again. This adaptation allows it to survive in environments with irregular water availability. Studies using
chlorophyll fluorescence Chlorophyll fluorescence is light re-emitted by chlorophyll molecules during return from Excited state, excited to non-excited states. It is used as an indicator of photosynthetic energy conversion in plants, algae and bacteria. Excited chlorop ...
measurements have shown that the species can recover rapidly and completely after spending a week in an air-dry state. When rehydrated, the plant's
photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...
apparatus returns to normal functioning within just two hours, regardless of whether recovery takes place in light or darkness. This rapid recovery suggests that ''P. platyphylla'' has "constitutive" protection mechanisms—meaning the protective systems are always present rather than being produced in response to drying. During drying, the plant's
photosynthetic efficiency The photosynthetic efficiency (i.e. ''oxygenic photosynthesis efficiency'') is the fraction of light energy converted into chemical energy during photosynthesis in green plants and algae. Photosynthesis can be described by the simplified chemical r ...
remains near optimal until water content falls below about half of the fully hydrated state, after which it declines steeply. However, this decline is fully reversible, and the period of desiccation appears as only a temporary interruption of normal photosynthetic function. The plant shows increased
photoprotection Photoprotection is the biochemical process that helps organisms cope with molecular damage caused by sunlight. Plants and other oxygenic phototrophs have developed a suite of photoprotective mechanisms to prevent photoinhibition and oxidative str ...
during recovery in light conditions, with these protective processes being essentially complete within 24 hours.


Chemistry

''Porella platyphylla'' produces a wide range of
terpenoid The terpenoids, also known as isoprenoids, are a class of naturally occurring organic compound, organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeabl ...
metabolites, including
mono Mono may refer to: Biology * Infectious mononucleosis, "the kissing disease" * Monocyte, a type of leukocyte (white blood cell) * Monodactylidae, members of which are referred to as monos Technology and computing * Mono (audio), single-c ...
-, sesqui-, di- and
triterpenoid Triterpenes are a class of terpenes composed of six isoprene units with the molecular formula C30H48; they may also be thought of as consisting of three terpene units. Animals, plants and fungi all produce triterpenes, including squalene, the pre ...
s. The species belongs to the "nonpungent"
chemotype A chemotype (sometimes chemovar) is a chemically distinct entity in a plant or microorganism, with differences in the composition of the secondary metabolites. Minor genetic and epigenetic changes with little or no effect on morphology or anatomy ...
of ''Porella'' species (referring to taste rather than smell), producing primarily pinguisane sesquiterpenoids and sacculatane diterpenoids – carbon skeletons that remain unique to liverworts. The species can be distinguished chemically from pungent ''Porella'' species, which produce intensely pungent drimane compounds and related substances. ''P. platyphylla'' belongs to the pinguisane-sacculatane chemotype, characterised by high amounts of pinguisane-type sesquiterpenoids alongside sacculatane-type diterpenoids. It is known for the presence of monoterpenoids, with α-terpinene as the most abundant component. Chemical composition shows strong correlation with molecular phylogenetic data in the genus ''Porella''. The chemical profile of ''P. platyphylla'' places it in a clade with ''P. navicularis'', both sharing the pinguisane-sacculatane chemotype. The absence of pungent drimane compounds distinguishes this clade from the ''P. vernicosa'' complex, which forms a distinct section within the genus characterised by pungent taste and glossy appearance. The chemical composition of ''Porella'' species, particularly their terpenoid profiles, has proven valuable for taxonomic investigations, helping to resolve uncertainties in this morphologically challenging genus through correlation with molecular data.


Distribution and habitat

''Porella platyphylla'' is widely distributed in forest ecosystems that receive at least 600 millimetres of annual precipitation. It is particularly abundant in northern and central Europe and along the Atlantic coast and islands, though it can also be found scattered throughout Mediterranean regions. The liverwort has a
Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical reg ...
distribution pattern, occurring across Eurasia and North America. The species shows distinct geographical structuring in its genetic makeup, with European and North American populations forming separate sister clades. While the species is capable of
long-distance dispersal Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal') and the movement from one breeding site to another ('breeding dispersal' ...
—as evidenced by its wide distribution—molecular evidence suggests that successful establishment and genetic mixing between distant populations remains relatively rare. Whilst the species is widespread in Europe, the typical European form (''P. platyphylla''
sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
) has been confirmed from only a single locality in New Mexico in North America. The species typically grows on tree bark and rocks, though habitat preferences may vary between different genetic lineages. The North American populations formerly known as ''P. platyphylloidea'' were historically noted to occur more frequently on rock substrates, whilst European populations were more commonly found on bark, though this distinction has proven unreliable for taxonomic purposes. In the southern part of the
Russian Far East The Russian Far East ( rus, Дальний Восток России, p=ˈdalʲnʲɪj vɐˈstok rɐˈsʲiɪ) is a region in North Asia. It is the easternmost part of Russia and the Asia, Asian continent, and is coextensive with the Far Easte ...
, it primarily occurs on
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
and other basic rocks in partly shaded conditions. However, in northern regions such as the
Commander Islands The Commander Islands, Komandorski Islands, or Komandorskie Islands (, ''Komandorskiye ostrova'') are a series of islands in the Russian Far East, a part of the Aleutian Islands, located about east of the Kamchatka Peninsula in the Bering Sea. ...
(around 55°N), it can be found on temporarily inundated stream beds, showing habitat preferences more similar to those seen in northern Europe. Within Russia, most occurrences lie between 43° and 45°N, though the species penetrates northward to several locations including the
Bolshoy Anyuy The Bolshoy Anyuy (; "Great Anyuy") is a river in the Kolyma (river), Kolyma basin in Far East Siberia. Administratively most of the basin of the Bolshoy Anyuy and its tributaries belong to the Chukotka Autonomous Okrug of Russia. Geography It flo ...
(49°N), Komsomolsk Nature Reserve (51°N), and the
Dzhagdy Range The Dzhagdy Range () is a range of mountains in far Russian Far East, North-eastern Russia. Administratively it belongs partly to Amur Oblast and partly to the Khabarovsk Krai of the Federal subjects of Russia, Russian Federation. Geography The ...
(~54°N). Its presence in the Commander Islands (at almost 55°N) appears to be
relict A relict is a surviving remnant of a natural phenomenon. Biology A relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas. Geology and geomorphology In geology, a r ...
ual, particularly notable as the species is absent from the intervening
Kamchatka The Kamchatka Peninsula (, ) is a peninsula in the Russian Far East, with an area of about . The Pacific Ocean and the Sea of Okhotsk make up the peninsula's eastern and western coastlines, respectively. Immediately offshore along the Pacific ...
Peninsula.


References

{{Taxonbar, from=Q905960 Porellales Plants described in 1753 Taxa named by Carl Linnaeus Flora of Europe Flora of Northern America Flora of Russia Epiphytes Lithophytes