Editing Moss (section)

==Physical characteristics==

===Description===

[[File:Bryum capillare leaf cells.jpg|thumb|left|Chloroplasts (green discs) and accumulated starch granules in cells of ''[[Bryum|Bryum capillare]]'']]

Botanically, mosses are [[non-vascular plant]]s in the land plant division Bryophyta. They are usually small (a few centimeters tall) [[Herbaceous plant|herbaceous]] (non-woody) plants that absorb water and nutrients mainly through their leaves and harvest [[carbon dioxide]] and sunlight to create food by [[photosynthesis]].<ref name=mathews /><ref name=pojar /> With the exception of the ancient group [[Takakia|Takakiopsida]], no known mosses form [[mycorrhiza]],<ref>{{Cite journal|url=https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2009.03137.x|title=Presence of three mycorrhizal genes in the common ancestor of land plants suggests a key role of mycorrhizas in the colonization of land by plants|first1=Bin|last1=Wang|first2=Li Huey|last2=Yeun|first3=Jia-Yu|last3=Xue|first4=Yang|last4=Liu|first5=Jean-Michel|last5=Ané|first6=Yin-Long|last6=Qiu|date=19 December 2010|journal=New Phytologist|volume=186|issue=2|pages=514–525|via=Wiley Online Library|doi=10.1111/j.1469-8137.2009.03137.x|pmid=20059702 |bibcode=2010NewPh.186..514W |hdl=2027.42/78704 |hdl-access=free}}</ref> but bryophilous fungi is widespread in moss and other bryophytes, where they live as saprotrophs, parasites, pathogens and mutualists, some of them [[endophyte]]s.<ref>{{Cite web|url=https://www.duo.uio.no/bitstream/handle/10852/11880/Heimdal.pdf?sequence=3|title=Using 454 sequencing for exploring diversity, host specificity and tissue specificity of the fungal genus Galerina associated with four boreal mosses}}</ref> Mosses differ from [[vascular plants]] in lacking water-bearing [[xylem]] [[tracheids]] or [[vessel elements|vessels]]. As in [[Marchantiophyta|liverworts]] and [[hornwort]]s, the [[haploid]] [[gametophyte]] generation is the dominant phase of the [[biological life cycle|life cycle]]. This contrasts with the pattern in all vascular plants ([[seed plants]] and [[pteridophytes]]), where the [[Haploid|diploid]] [[sporophyte]] generation is dominant. Mosses reproduce using [[spore]]s, not [[seed]]s, and have no flowers.

[[File:Moss leaf under microscope.jpg|thumb|upright=0.9|Moss leaf under microscope, showing [[Gemma (botany)|gemmae]] and a hair point (40x)]]

Moss gametophytes have stems which may be simple or branched and upright (acrocarp) or prostrate (pleurocarp). The early divergent classes Takakiopsida, Sphagnopsida, Andreaeopsida and Andreaeobryopsida either lack [[stoma]]ta or have pseudostomata that do not form pores. In the remaining classes, stomata have been lost more than 60 times.<ref>{{Cite journal|title=With Over 60 Independent Losses, Stomata Are Expendable in Mosses|first1=Karen S.|last1=Renzaglia|first2=William B.|last2=Browning|first3=Amelia|last3=Merced|date=28 May 2020|journal=Frontiers in Plant Science|volume=11|page=567 |doi=10.3389/fpls.2020.00567|doi-access=free |pmid=32547571 |pmc=7270291 |bibcode=2020FrPS...11..567R }}</ref> Their leaves are simple, usually only a single layer of cells with no internal air spaces, often with thicker midribs (nerves). The nerve can run beyond the edge of the leaf tip, termed excurrent. The tip of the leaf blade can be extended as a hair point, made of colourless cells. These appear white against the dark green of the leaves. The edge of the leaf can be smooth or it may have teeth. There may be a distinct type of cell defining the edge of the leaf, distinct in shape and/or colour from the other leaf cells.<ref name="BBS - field guide2010">{{cite book |last1=Atherton |first1=Ian |last2=Bosanquet |first2=Sam |last3=Lawley |first3=Mark |title=Mosses and Liverworts of Britain and Ireland - a field guide |date=2010 |publisher=British Bryological Society |isbn=9780956131010 |pages=848}}</ref>

Moss has threadlike [[rhizoids]] that anchor them to their substrate, comparable to [[root hairs]] rather than the more substantial [[root]] structures of [[spermatophytes]].<ref name="Watson1981">{{cite book |last1=Watson |first1=E. Vernon |title=British Mosses and Liverworts |date=1981 |publisher=Cambridge University Press |isbn=052129472X |pages=519 |edition=3rd}}</ref> Mosses do not absorb water or nutrients from their substrate through their rhizoids.{{citation needed|date=April 2020}} They can be distinguished from [[Marchantiophyta|liverworts]] ([[Marchantiophyta]] or Hepaticae) by their multi-cellular rhizoids. Spore-bearing capsules or [[sporangium|sporangia]] of mosses are borne singly on long, unbranched stems, thereby distinguishing them from the [[polysporangiophytes]], which include all vascular plants. The spore-producing sporophytes (i.e. the [[diploid]] multicellular generation) are short-lived and usually capable of photosynthesis, but are dependent on the gametophyte for water supply and most or all of its nutrients.<ref name=Budke-2018>{{cite journal |first1=Jessica M |last1=Budke |first2=Ernest C |last2=Bernard |first3=Dennis J |last3=Gray |first4=Sanna |last4=Huttunen |first5=Birgit |last5=Piechulla |first6=Robert N |last6=Trigiano |date=2018 |title=Introduction to the special issue on bryophytes |journal=Critical Reviews in Plant Sciences |volume=37 |issue=2–3 |pages=102–112 |doi=10.1080/07352689.2018.1482396 |bibcode=2018CRvPS..37..102B }}</ref> Also, in the majority of mosses, the spore-bearing capsule enlarges and matures after its stalk elongates, while in liverworts the capsule enlarges and matures before its stalk elongates.<ref name=pojar /> Other differences are not universal for all mosses and all liverworts, but the presence of a clearly differentiated stem with simple-shaped, non-vascular leaves that are not arranged in three ranks, all point to the plant being a moss.{{citation needed|date=April 2023}}

===Life cycle===
<!-- This section is linked from "Alternation of generations"; be sure to change the link there if you change the title of this section. -->

Vascular [[plant]]s have two sets of [[chromosome]]s in their vegetative cells and are said to be [[diploid]], i.e. each chromosome has a partner that contains the same, or similar, genetic information. By contrast, mosses and other [[bryophyte]]s have only a single set of chromosomes and so are [[haploid]] (i.e. each chromosome exists in a unique copy within the cell). There is a period in the moss life cycle when they do have a double set of paired chromosomes, but this happens only during the [[sporophyte]] stage.

[[File:Lifecycle moss svg diagram.svg|thumb|300px|Life cycle of a typical moss (''[[Polytrichum commune]]'')]]

The moss life-cycle starts with a haploid [[spore]] that germinates to produce a [[protonema]] (''pl.'' protonemata), which is either a mass of thread-like filaments or thalloid (flat and thallus-like). Massed moss protonemata typically look like a thin green felt, and may grow on damp soil, tree bark, rocks, concrete, or almost any other reasonably stable surface. This is a transitory stage in the life of a moss, but from the protonema grows the [[gametophore]] ("gamete-bearer") that is structurally differentiated into stems and leaves. A single mat of protonemata may develop several gametophore shoots, resulting in a clump of moss.

From the tips of the gametophore stems or branches develop the sex organs of the mosses. The female organs are known as [[archegonia]] (''sing.'' [[archegonium]]) and are protected by a group of modified leaves known as the perichaetum (plural, perichaeta). The archegonia are small flask-shaped clumps of cells with an open neck (venter) down which the male sperm swim. The male organs are known as [[antheridia]] (''sing.'' [[antheridium]]) and are enclosed by modified leaves called the perigonium (''pl.'' perigonia). The surrounding leaves in some mosses form a splash cup, allowing the sperm contained in the cup to be splashed to neighboring stalks by falling water droplets.<ref name="vanderVelde2001" />

Gametophore tip growth is disrupted by fungal [[chitin]].<ref name="Delaux-Schornack-2021">{{cite journal | last1=Delaux | first1=Pierre-Marc | last2=Schornack | first2=Sebastian | title=Plant evolution driven by interactions with symbiotic and pathogenic microbes | journal=[[Science (journal)|Science]] | publisher=[[American Association for the Advancement of Science]] (AAAS) | volume=371 | issue=6531 | date=2021-02-19 | issn=0036-8075 | doi=10.1126/science.aba6605 | pages=1–10 | pmid=33602828 | s2cid=231955632| url=https://hal.archives-ouvertes.fr/hal-03327916/file/Delaux%20Schornack%20-%20HAL.pdf }}</ref><ref name="Bibeau-et-al-2021">{{cite journal | last1=Bibeau | first1=Jeffrey P. | last2=Galotto | first2=Giulia | last3=Wu | first3=Min | last4=Tüzel | first4=Erkan | last5=Vidali | first5=Luis | title=Quantitative cell biology of tip growth in moss | journal=[[Plant Molecular Biology]] | publisher=[[Springer Science+Business Media|Springer]] | volume=107 | issue=4–5 | date=2021-04-06 | issn=0167-4412 | doi=10.1007/s11103-021-01147-7 | pages=227–244| pmid=33825083 | pmc=8492783 | bibcode=2021PMolB.107..227B }}</ref><ref name="Sun-et-al-2020">{{cite journal | last1=Sun | first1=Guiling | last2=Bai | first2=Shenglong | last3=Guan | first3=Yanlong | last4=Wang | first4=Shuanghua | last5=Wang | first5=Qia | last6=Liu | first6=Yang | last7=Liu | first7=Huan | last8=Goffinet | first8=Bernard | last9=Zhou | first9=Yun | last10=Paoletti | first10=Mathieu | last11=Hu | first11=Xiangyang | last12=Haas | first12=Fabian B. | last13=Fernandez-Pozo | first13=Noe | last14=Czyrt | first14=Alia | last15=Sun | first15=Hang | last16=Rensing | first16=Stefan A. | last17=Huang | first17=Jinling | title=Are fungi-derived genomic regions related to antagonism towards fungi in mosses? | journal=[[New Phytologist]] | publisher=New Phytologist Foundation ([[Wiley publishing|Wiley]]) | volume=228 | issue=4 | date=2020-07-31 | issn=0028-646X | doi=10.1111/nph.16776 | pages=1169–1175 | pmid=32578878 | s2cid=220047618| doi-access=free | bibcode=2020NewPh.228.1169S }}</ref> Galotto ''et al.'', 2020 applied [[chitooctaose]] and found that tips detected and responded to this chitin derivative by changing [[gene expression]].<ref name="Delaux-Schornack-2021" /><ref name="Bibeau-et-al-2021" /><ref name="Sun-et-al-2020" /> They concluded that this defense response was probably [[conserved sequence|conserved]] from the [[most recent common ancestor]] of [[bryophyte]]s and [[tracheophytes]].<ref name="Delaux-Schornack-2021" /> Orr ''et al.'', 2020 found that the [[microtubule]]s of growing tip cells were structurally similar to [[F-actin]] and served a similar purpose.<ref name="Bibeau-et-al-2021" />

Mosses can be either [[dioicous]] (compare [[dioecious]] in seed plants) or [[monoicous]] (compare [[monoecious]]). In dioicous mosses, male and female sex organs are borne on different gametophyte plants. In monoicous (also called autoicous) mosses, both are borne on the same plant. In the presence of water, sperm from the antheridia swim to the archegonia and [[fertilisation]] occurs, leading to the production of a diploid sporophyte. The sperm of mosses is biflagellate, i.e. they have two flagellae that aid in propulsion. Since the sperm must swim to the archegonium, fertilisation cannot occur without water. Some species (for example ''Mnium hornum'' or several species of ''Polytrichum'') keep their antheridia in so called 'splash cups', bowl-like structures on the shoot tips that propel the sperm several decimeters when water droplets hit it, increasing the fertilization distance.<ref name="vanderVelde2001">{{Cite journal|title = The reproductive biology of Polytrichum formosum: clonal structure and paternity revealed by microsatellites|last1 = van der Velde|first1 = M.|journal = Molecular Ecology|doi = 10.1046/j.0962-1083.2001.01385.x|pmid = 11742546|issue = 10|pages = 2423–2434|last2 = During|first2 = H. J.|last3 = van de Zande|first3 = L.|last4 = Bijlsma|first4 = R.|volume = 10|year = 2001| bibcode=2001MolEc..10.2423V |s2cid = 19716812}}</ref>

After fertilisation, the immature sporophyte pushes its way out of the archegonial venter. It takes several months for the [[sporophyte]] to mature. The sporophyte body comprises a long stalk, called a seta, and a capsule capped by a cap called the [[Operculum (Botany)|operculum]]. The capsule and operculum are in turn sheathed by a haploid calyptra which is the remains of the archegonial venter. The calyptra usually falls off when the capsule is mature. Within the capsule, spore-producing cells undergo [[meiosis]] to form haploid spores, upon which the cycle can start again. The mouth of the capsule is usually ringed by a set of teeth called peristome. This may be absent in some mosses.{{citation needed|date=April 2023}}

Most mosses rely on the wind to disperse the spores. In the [[genus]] ''[[Sphagnum]]'' the [[Sphagnum#Spore dispersal|spores are projected]] about {{Convert|10-20|cm|4 = 0|abbr = on}} off the ground by compressed air contained in the capsules; the spores are accelerated to about 36,000 times the [[Gravity of Earth|earth's gravitational acceleration ''g'']].<ref>{{cite journal|doi= 10.1126/science.1193047|author= Johan L. van Leeuwen |title= Launched at 36,000''g'' |journal=Science|pages= 395–6|issue= 5990 |volume= 329 |date= July 23, 2010|pmid= 20651138|s2cid= 206527957 }}</ref><ref>{{cite journal|doi= 10.1126/science.1190179|author1=Dwight K. Whitaker  |author2=Joan Edwards  |name-list-style=amp |title= ''Sphagnum'' Moss Disperses Spores with Vortex Rings |journal=Science|page= 406|issue= 5990 |volume= 329 |date= July 23, 2010|pmid= 20651145|bibcode=2010Sci...329..406W |s2cid=206526774 }}</ref>

[[File:Moss Gametophytes Sporophytes.JPG|thumb|300px|A patch of moss showing both gametophytes (the low, leaf-like forms) and sporophytes (the tall, stalk-like forms)]]

It has recently been found that microarthropods, such as [[springtails]] and [[mites]], can effect moss fertilization<ref name="cronberg2006">{{Cite journal | last1 = Cronberg | first1 = N. | last2 = Natcheva | first2 = R. | last3 = Hedlund | first3 = K. | doi = 10.1126/science.1128707 | title = Microarthropods Mediate Sperm Transfer in Mosses | journal = Science | volume = 313 | issue = 5791 | pages = 1255 | year = 2006 | pmid =  16946062| s2cid = 11555211 }}</ref> and that this process is mediated by moss-emitted scents. Male and female [[fire moss]], for example, emit different and complex volatile organic scents.<ref name="rosenstiel2012">{{Cite journal | last1 = Rosenstiel | first1 = T. N. | last2 = Shortlidge | first2 = E. E. | last3 = Melnychenko | first3 = A. N. | last4 = Pankow | first4 = J. F. | last5 = Eppley | first5 = S. M. | title = Sex-specific volatile compounds influence microarthropod-mediated fertilization of moss | doi = 10.1038/nature11330 | journal = Nature | volume = 489 | issue = 7416 | pages = 431–433 | year = 2012 | pmid =  22810584| bibcode = 2012Natur.489..431R | s2cid = 4419337 }}</ref> Female plants emit more compounds than male plants. [[Springtails]] were found to choose female plants preferentially, and one study found that springtails enhance moss fertilization, suggesting a scent-mediated relationship analogous to the plant-pollinator relationship found in many seed plants.<ref name="rosenstiel2012" /> The stinkmoss species ''[[Splachnum sphaericum]]'' develops insect pollination further by attracting flies to its sporangia with a strong smell of carrion, and providing a strong visual cue in the form of red-coloured swollen collars beneath each spore capsule. Flies attracted to the moss carry its spores to fresh herbivore dung, which is the favoured habitat of the species of this genus.<ref name=vaizey>{{cite journal | last1 = Vaizey | first1 = J. R. | year = 1890 | title = On the Morphology of the Sporophyte of ''Splachnum luteum'' | journal = Annals of Botany | volume = 1 | pages = 1–8 | doi = 10.1093/oxfordjournals.aob.a090623 }}</ref>

In many mosses, e.g., ''Ulota phyllantha'', green vegetative structures called [[gemma (botany)|gemmae]] are produced on leaves or branches, which can break off and form new plants without the need to go through the cycle of fertilization. This is a means of [[asexual reproduction]], and the genetically identical units can lead to the formation of [[cloning|clonal]] populations.

===Dwarf males===
Moss dwarf males (also known as [[nannandry]] or [[phyllodioicy]]) originate from wind-dispersed male [[spore]]s that settle and germinate on the female shoot where their growth is restricted to a few millimeters. In some species, dwarfness is genetically determined, in that all male spores become dwarf.<ref name="UneKouji">{{Cite journal|url = http://ir.lib.osaka-kyoiku.ac.jp/dspace/handle/123456789/2572|title = Sexual dimorphism in the Japanese species of Macromitrium Brid.(Musci: Orthotrichaceae)|last = Une|first = Kouji|journal = The Journal of the Hattori Botanical Laboratory Devoted to Bryology and Lichenology|pages = 487–513|year = 1985|volume = 59}}</ref> More often, it is environmentally determined in that male spores that land on a female become dwarf, while those that land elsewhere develop into large, female-sized males.<ref name="UneKouji" /><ref>{{Cite journal|title = The male gametophores of Leucobryum glaucum (Hedw.) Ångstr. and L. juniperoideum (Brid.) C. Muell. in two Welsh woodlands|last = Blackstock|first = T. H.|journal = Journal of Bryology|doi = 10.1179/jbr.1987.14.3.535|year = 1987|pages = 535–541|issue = 3|volume = 14| bibcode=1987JBryo..14..535B }}</ref><ref name="Loveland">{{Cite book|title = Sexual dimorphism in the moss genus Dicranum Hedw. (Dissertation)|last = Loveland|first = Hugh Frank|publisher = University of Michigan|year = 1956}}</ref><ref name="Wallace">{{Cite book|title = Developmental morphology and sexual dimorphism in Homalothecium megaptilum (Sull.) Robins. (Dissertation)|last = Wallace|first = M. H.|publisher = Washington State University|year = 1970}}</ref> In the latter case, dwarf males that are transplanted from females to another substrate develop into large shoots, suggesting that the females emit a substance which inhibits the growth of germinating males and possibly also quickens their onset of sexual maturation.<ref name="Loveland" /><ref name="Wallace" /> The nature of such a substance is unknown, but the phytohormone [[auxin]] may be involved<ref name="UneKouji" />

Having the males growing as dwarfs on the female is expected to increase the [[fertilization]] efficiency by minimizing the distance between male and female reproductive organs. Accordingly, it has been observed that fertilization frequency is positively associated with the presence of dwarf males in several [[phyllodioicy|phyllodioicous]] species.<ref>{{Cite journal|title = Studies of fertility of Dicranum majus in two populations with contrasted sporophyte production|last1 = Sagmo Solli|first1 = I. M.|journal = Journal of Bryology|doi =10.1179/jbr.2000.22.1.3 |year =1998 |pages =3–8 |issue =1 |volume = 22|last2 = Söderström|first2 = Lars|last3 = Bakken|first3 = Solveig|last4 = Flatberg|first4 = Kjell Ivar|last5 = Pedersen|first5 = Bård|s2cid = 85349694}}</ref><ref name="Hedenäs">{{Cite journal|title = The overlooked dwarf males in mosses—unique among green land plants|last1 = Hedenäs|first1 = Lars|journal = Perspectives in Plant Ecology, Evolution and Systematics|doi =10.1016/j.ppees.2011.03.001 |year = 2011|pages = 121–135|issue = 2|last2 = Bisang|first2 = Irene|volume = 13| bibcode=2011PPEES..13..121H }}</ref>

Dwarf males occur in several unrelated [[Lineage (evolution)|lineages]]<ref name="Hedenäs" /><ref>{{Cite journal|title = Sex determination in bryophytes|last1 = Ramsay|first1 = Helen P.|journal = Journal of the Hattori Botanical Laboratory|volume = 52|year = 1982|pages = 255–274|last2 = Berrie|first2 = G. K.}}</ref> and may be more common than previously thought.<ref name="Hedenäs" /> For example, it is estimated that between one quarter and half of all [[dioicy|dioicous]] [[pleurocarpous|pleurocarp]]s have dwarf males.<ref name="Hedenäs" />

===DNA repair===
The moss ''[[Physcomitrium patens]]'' has been used as a [[model organism]] to study how plants [[DNA repair|repair]] damage to their DNA, especially the repair mechanism known as [[homologous recombination]]. If the plant cannot repair DNA damage, e.g., [[double-strand breaks]], in their [[somatic cell]]s, the cells can lose normal functions or die. If this occurs during [[meiosis]] (part of sexual reproduction), they could become infertile. The genome of ''P. patens'' has been sequenced, which has allowed several genes involved in DNA repair to be identified.<ref name="pmid18079367">{{cite journal |last1=Rensing |first1=S.A. |last2=Lang |first2=D |last3=Zimmer |first3=A.D. |last4=Terry |first4=A. |last5=Salamov |first5=A |last6=Shapiro |first6=H. |last7=Nishiyama |first7=T. |last8=Sakakibara  |first8=K. |display-authors=7 |title=The Physcomitrella genome reveals evolutionary insights into the conquest of land by plants |journal=Science |volume=319 |issue=5859 |pages=64–9 | date=January 2008 |pmid=18079367 |doi=10.1126/science.1150646 |url=http://pubman.mpdl.mpg.de/pubman/item/escidoc:1221568/component/escidoc:1221567/rensing_et_al_science_2008.pdf|hdl=11858/00-001M-0000-0012-3787-A |bibcode=2008Sci...319...64R |s2cid=11115152 |hdl-access=free }}</ref> ''P. patens'' mutants that are defective in key steps of homologous recombination have been used to work out how the repair mechanism functions in plants. For example, a study of ''P. patens'' mutants defective in ''Rp''RAD51, a gene that encodes a protein at the core of the recombinational repair reaction, indicated that homologous recombination is essential for repairing DNA double-strand breaks in this plant.<ref name="pmid17921313">{{cite journal |vauthors=Markmann-Mulisch U, Wendeler E, Zobell O, Schween G, Steinbiss HH, Reiss B |title=Differential requirements for RAD51 in Physcomitrella patens and Arabidopsis thaliana development and DNA damage repair |journal=Plant Cell |volume=19 |issue=10 |pages=3080–9 | date=October 2007 |pmid=17921313 |pmc=2174717 |doi=10.1105/tpc.107.054049 |bibcode=2007PlanC..19.3080M }}</ref> Similarly, studies of mutants defective in ''Ppmre11'' or ''Pprad50'' (that encode key proteins of the [[MRN complex]], the principal sensor of DNA double-strand breaks) showed that these genes are necessary for repair of DNA damage as well as for normal growth and development.<ref name="pmid22210882">{{cite journal |vauthors=Kamisugi Y, Schaefer DG, Kozak J, Charlot F, Vrielynck N, Holá M, Angelis KJ, Cuming AC, Nogué F |title=MRE11 and RAD50, but not NBS1, are essential for gene targeting in the moss Physcomitrella patens |journal=Nucleic Acids Res. |volume=40 |issue=8 |pages=3496–510 | date=April 2012 |pmid=22210882 |pmc=3333855 |doi=10.1093/nar/gkr1272 }}</ref>