Examine individual changes

':''This article is about the non-vascular plants. The name Hornwort also refers to aquatic plants of the genus ''[[Ceratophyllum]]'', in the family Ceratophyllaceae''. {{Taxobox | fossil_range = {{fossil range|90|0}}Upper [[Cretaceous]] (but see text) to recent | name = Hornwort | image = Phaeoceros laevis.jpg | image_width = 240px | image_caption = ''Phaeoceros laevis'' ([[Carolus Linnaeus|L.]]) [[Johannes Max Proskauer|Prosk.]] | regnum = [[Plant]]ae | divisio = '''Anthocerotophyta''' | divisio_authority = Stotler & Stotl.-Crand.<ref>{{cite journal | last = Stotler | first = Raymond E. | coauthors = Barbara J. Candall-Stotler | year = 1977 | title = A checklist of the liverworts and hornworts of North America | journal = The Bryologist | volume=80 | pages=405–428 | doi = 10.2307/3242017 | issue = 3 | publisher = American Bryological and Lichenological Society | jstor = 3242017 }}</ref> | subdivision_ranks = [[Class (biology)|Classes]] & [[Order (biology)|Orders]] | subdivision = ;Leiosporocerotopsida * [[Leiosporoceros|Leiosporocerotales]] ;Anthocerotopsida * [[Anthocerotaceae|Anthocerotales]] * [[Dendrocerotaceae|Dendrocerotales]] * [[Notothyladaceae|Notothyladales]] * [[Phymatoceros|Phymatocerotales]] ''see [[#Classification|Classification]]''. | synonyms = Anthocerotae }} '''Hornworts''' are a group of [[bryophyte]]s, or [[non-vascular plant]]s, comprising the division '''Anthocerotophyta'''. The common name refers to the elongated horn-like structure, which is the [[sporophyte]]. The flattened, green plant body of a hornwort is the [[gametophyte]] plant. Hornworts may be found worldwide, though they tend to grow only in places that are damp or humid. Some species grow in large numbers as tiny weeds in the soil of gardens and cultivated fields. Large tropical and sub-tropical species of ''Dendroceros'' may be found growing on the bark of trees. ==Description == The plant body of a hornwort is a [[haploid]] [[gametophyte]] stage. This stage usually grows as a thin [[rosette (botany)|rosette]] or ribbon-like [[thallus]] between one and five centimeters in diameter. Each [[cell (biology)|cell]] of the thallus usually contains just one [[chloroplast]]. In most [[species]], this chloroplast is fused with other [[organelle]]s to form a large [[pyrenoid]] that both manufactures and stores food. This particular feature is very unusual in land [[plant]]s, but is common among [[alga]]e. Many hornworts develop internal [[mucilage]]-filled cavities when groups of cells break down. These cavities are invaded by [[photosynthetic]] [[cyanobacteria]], especially species of ''[[Nostoc]]''. Such colonies of bacteria growing inside the thallus give the hornwort a distinctive blue-green color. There may also be small ''slime pores'' on the underside of the thallus. These pores superficially resemble the [[stomata]] of other plants. The horn-shaped [[sporophyte]] grows from an [[archegonium]] embedded deep in the gametophyte. The sporophyte of a hornwort is unusual in that it grows from a [[meristem]] near its base, instead of from its tip the way other [[plant]]s do. Unlike [[Marchantiophyta|liverworts]], most hornworts have true [[stoma]]ta on their sporophyte as mosses do. The exceptions are the [[genus|genera]] ''[[Notothylas]]'' and ''[[Megaceros]]'', which do not have stomata. When the sporophyte is mature, it has a multicellular outer layer, a central rod-like [[columella (botany)|columella]] running up the center, and a layer of [[tissue (biology)|tissue]] in between that produces spores and [[elater|pseudo-elaters]]. The pseudo-elaters are multi-cellular, unlike the elaters of [[Marchantiophyta|liverwort]]s. They have [[helical]] thickenings that change shape in response to drying out; they twist and thereby help to disperse the spores. Hornwort spores are relatively large for [[bryophyte]]s, measuring between 30 and 80 [[micrometre|µm]] in diameter or more. The spores are polar, usually with a distinctive Y-shaped tri-radiate ridge on the [[proximal]] surface, and with a [[distal]] surface ornamented with bumps or spines. == 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. --> The life of a hornwort starts from a [[haploid]] spore. In most species, there is a single cell inside the spore, and a slender extension of this cell called the ''germ tube'' germinates from the proximal side of the spore.<ref name="Chopra 1988">{{ cite book | last=Chopra | first=R. N. | coauthor=Kumra, P. K. | year=1988 | title=Biology of Bryophytes | location= New York | publisher=John Wiley & Sons | isbn=0-470-21359-0 }}</ref> The tip of the germ tube divides to form an [[octant]] of cells, and the first [[rhizoid]] grows as an extension of the original germ cell. The tip continues to divide new cells, which produces a thalloid [[protonema]]. By contrast, species of the family [[Dendrocerotaceae]] may begin dividing within the spore, becoming [[multicellular]] and even [[photosynthetic]] before the spore germinates.<ref name="Chopra 1988" /> In either case, the protonema is a transitory stage in the life of a hornwort. [[Image:Hornwort life cycle.svg|thumb|300px|left|Life cycle of a typical hornwort ''Phaeoceros''. Click on the image to enlarge.]] From the protonema grows the adult [[gametophyte]], which is the persistent and independent stage in the life cycle. This stage usually grows as a thin [[rosette (botany)|rosette]] or ribbon-like [[thallus]] between one and five centimeters in diameter, and several layers of cells in thickness. It is green or yellow-green from the [[chlorophyll]] in its cells, or bluish-green when colonies of cyanobacteria grow inside the plant. When the gametophyte has grown to its adult size, it produces the sex organs of the hornwort. Most plants are [[Bryophyte|monoicous]], with both sex organs on the same plant, but some plants (even within the same species) are [[Bryophyte|dioicous]], with separate male and female gametophytes. The female organs are known as [[archegonium|archegonia]] (singular archegonium) and the male organs are known as [[antheridium|antheridia]] (singular antheridium). Both kinds of organs develop just below the surface of the plant and are only later exposed by disintegration of the overlying cells. The biflagellate [[spermatozoon|sperm]] must swim from the antheridia, or else be splashed to the archegonia. When this happens, the sperm and egg cell fuse to form a [[zygote]], the cell from which the sporophyte stage of the life cycle will develop. Unlike all other bryophytes, the first cell division of the zygote is [[Anatomical terms of location|longitudinal]]. Further divisions produce three basic regions of the sporophyte. At the bottom of the [[sporophyte]] (closest to the interior of the gametophyte), is a foot. This is a globular group of cells that receives nutrients from the parent gametophyte, on which the sporophyte will spend its entire existence. In the middle of the sporophyte (just above the foot), is a [[meristem]] that will continue to divide and produce new cells for the third region. This third region is the [[Sporangia|capsule]]. Both the central and surface cells of the capsule are sterile, but between them is a layer of cells that will divide to produce [[elater|pseudo-elaters]] and [[spore]]s. These are released from the capsule when it splits lengthwise from the tip. ==Evolutionary history== {{Expand section|date=June 2008}} While the fossil record of [[crown group]] hornworts only begins in the upper [[Cretaceous]], the lower Devonian ''[[Horneophyton]]'' may represent a stem group to the clade, as it possesses a [[sporangium]] with central columella not attached at the roof.<ref name=Qiu2006>{{cite journal | author = Qiu, Y.L. | coauthors = Li, L.; Wang, B.; Chen, Z.; Knoop, V.; Groth-malonek, M.; Dombrovska, O.; Lee, J.; Kent, L.; Rest, J.; Others, | year = 2006 | title = The deepest divergences in land plants inferred from phylogenomic evidence | journal = Proceedings of the National Academy of Sciences | volume = 103 | issue = 42 | pages = 15511–6 | doi = 10.1073/pnas.0603335103 | pmid = 17030812 | pmc = 1622854 }}</ref> However, the same form of columella is also characteristic of basal moss groups, such as the [[Sphagnopsida]] and [[Andreaeopsida]], and has been interpreted as a character common to all early land plants with [[stoma]]ta.<ref>{{cite book | last=Kenrick | first=Paul |coauthors=Peter R. Crane | year=1997 | title= The Origin and Early Diversification of Land Plants: A Cladistic Study | location=Washington, D. C. | publisher= Smithsonian Institution Press | pages=55–56 | isbn=1-56098-730-8 }}</ref> == Classification == [[Image:Dendroceros.jpg|thumb|200px|The hornwort ''[[Dendroceros]] crispus'' growing on the bark of a tree.]] Hornworts were traditionally considered a class within the division Bryophyta ([[bryophyte]]s). However, it now appears that this former division is [[paraphyletic]], so the hornworts are now given their own division, '''Anthocerotophyta'''. The division [[bryophyte|Bryophyta]] is now restricted to include only [[moss]]es. Traditionally, there is a single class of hornworts, called '''Anthocerotopsida''', or older '''Anthocerotae'''. More recently, a second class Leiosporocertotopsida has been segregated for the singularly unusual species ''[[Leiosporoceros dussii]]''. All other hornworts remain in the class Anthocerotopsida. These two classes are divided further into five [[Order (biology)|orders]], each containing a single [[Family (biology)|family]]. Among land plants, hornworts appear to be one of the oldest surviving lineages; cladistic analysis implies that the group originated prior to the [[Devonian]], around the same time as the mosses and liverworts. There are only about 100 [[species]] known, but new species are still being discovered. The number and names of [[genus|genera]] are a current matter of investigation, and several competing classification schemes have been published since 1988. === Phylogeny === Recent studies of molecular, ultrastructural, and morphological data have yielded a new classification of hornworts.<ref name="Duff 2007">{{cite journal | last = Duff | first = R. Joel | coauthors = Juan Carlos Villarreal, D. Christine Cargill, & Karen S. Renzaglia | year = 2007 | title = Progress and challenges toward a phylogeny and classification of the hornworts | journal = The Bryologist | volume=110 | issue=2 | pages=214–243 | doi = 10.1639/0007-2745(2007)110[214:PACTDA]2.0.CO;2 }}</ref> {| align="left" style="text-align:left; padding:2.5px; background:#eef" |- | style="background:#fff; padding:2.5px; font-size:85%" |order '''Leiosporocerotales''' : '''[[Leiosporocerotaceae]]''' :* ''[[Leiosporoceros]]'' (1 species) order '''Anthocerotales''' : '''[[Anthocerotaceae]]''' :* ''[[Anthoceros]]'' (ca. 83 species) :* ''[[Folioceros]]'' (17 species) :* ''[[Sphaerosporoceros]]'' (2 species) order '''Notothyladales''' : '''[[Notothyladaceae]]''' :* ''[[Notothylas]]'' (21 species) :* ''[[Phaeoceros]]'' (ca. 41 species) :* ''[[Paraphymatoceros]]'' (1-2 species) :* ''[[Hattorioceros]]'' (1 species) :* ''[[Mesoceros]]'' (2 species) order '''Phymatocerotales''' : '''[[Phymatocerotaceae]]''' :* ''[[Phymatoceros]]'' (2 species) order '''Dendrocerotales''' : '''[[Dendrocerotaceae]]''' :* ''[[Dendroceros]]'' (43 species) :* ''[[Megaceros]]'' (8 species) :* ''[[Nothoceros]]'' (7 species) :* ''[[Phaeomegaceros]]'' (7 species) |{{clade| style=font-size:100%;line-height:100% |1={{clade |1={{clade |1={{clade |label1=[[Leiosporoceros|Leiosporocerotaceae]] |1=''[[Leiosporoceros]]'' }} }} |2={{clade |1={{clade |label1=[[Anthocerotaceae]] |1={{clade |1=''[[Folioceros]]'' |2={{clade |1=''[[Sphaerosporoceros]]'' |2=''[[Anthoceros]]'' }} }} }} }} |3={{clade |1={{clade |label1=[[Notothyladaceae]] |1={{clade |1=''[[Notothylas]]'' |2=''[[Phaeoceros]]'' }} }} |2={{clade |label1=[[Phymatoceros|Phymatocerotaceae]] |1=''[[Phymatoceros]]'' |label2=[[Dendrocerotaceae]] |2={{clade |1=''[[Phaeomegaceros]]'' |2={{clade |1=''[[Nothoceros]]'' |2={{clade |1=''[[Megaceros]]'' |2=''[[Dendroceros]]'' }} }} }} }} }} }} }} |-style="font-size:90%;" | colspan=2 | The current [[phylogenetics|phylogeny]] and composition of the Anthocerotophyta.<ref name="Duff 2007" /><ref name="Villarreal Phytotaxa">{{cite journal | last=Villareal | first=J. C. | coauthors=Cargill, D. C.; Hagborg, A.; Söderström, L.; Renzaglia, K. S. | title=A synthesis of hornwort diversity: Patterns, causes and future work | journal=Phytotaxa | volume=9 | pages=150–166 | url=http://mapress.com/phytotaxa/content/2010/f/pt00009p166.pdf | format=pdf }}</ref> |}{{-}} == See also == * [[Embryophyte]] == References == {{Reflist}} * {{Cite journal | last = Grolle | first = Riclef | year = 1983 | title = Nomina generica Hepaticarum; references, types and synonymies | journal = Acta Botanica Fennica | volume = 121 | pages = 1–62 }} * {{Cite journal | last = Hasegawa | first = J. | year = 1994 | title = New classification of Anthocerotae | journal = Journal of the Hattori Botanical Laboratory | volume = 76 | issue = | pages = 21–34 }} * {{Cite journal | last = Renzaglia | first = Karen S. | year = 1978 | title = A comparative morphology and developmental anatomy of the Anthocerotophyta | journal = Journal of the Hattori Botanical Laboratory | volume = 44 | issue = | pages = 31–90 }} * Renzaglia, Karen S. & Vaughn, Kevin C. (2000). Anatomy, development, and classification of hornworts. In A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology'', pp.&nbsp;1–20. Cambridge: [[Cambridge University Press]]. ISBN 0-521-66097-1. * {{cite book | last=Schofield | first=W. B. | year=1985 | title=Introduction to Bryology | location=New York | publisher=Macmillan}} * {{cite book | last=Schuster | first=Rudolf M. | year=1992 | title=The Hepaticae and Anthocerotae of North America, East of the Hundredth Meridian | volume=VI | location=Chicago | publisher=[[Field Museum of Natural History]] }} * {{cite book | last=Smith | first=Gilbert M. | year=1938 | title=Cryptogamic Botany, Volume II: Bryophytes and Pteridophytes | location=New York | publisher=McGraw-Hill Book Company }} * {{cite book | last=Watson | first=E. V. | year=1971 | title=The Structure and Life of Bryophytes | edition=3rd | location=London | publisher=Hutchinson University Library | isbn=0-09-109301-5 }} == External links == {{wikispecies|Anthocerotophyta}} {{Commons category|Anthocerotophyta}} * [http://www3.uakron.edu/biology/hornworts/hornworts.html Hornwort Web Portal] * [http://www.ucmp.berkeley.edu/plants/anthocerotophyta.html Anthocerotophyta description and fossil history at UCMP] * [http://www.eeb.uconn.edu/people/goffinet/Classificationhornworts.html Classification of the Anthocerotophyta] * [http://www.peripatus.gen.nz/Taxa/Bryophyta/NZAnthocerotae.html New Zealand Anthocerotae] {{Plant classification}} [[Category:Hornworts| ]] [[af:Horingblad]] [[az:Antoserot]] [[bg:Рогоспорангиеви мъхове]] [[ca:Antocerota]] [[cs:Hlevíky]] [[cy:Anthocerotophyta]] [[da:Hornblade]] [[de:Hornmoose]] [[et:Kõdersammaltaimed]] [[es:Anthocerotophyta]] [[eo:Antocerotoj]] [[fa:شاخ‌واش]] [[fr:Anthocerotophyta]] [[ko:뿔이끼류]] [[id:Lumut tanduk]] [[it:Anthocerotophyta]] [[he:אנתוצרוטה]] [[lt:Ylvaisainiai]] [[hu:Becősmohák]] [[mk:Роговница]] [[ja:ツノゴケ類]] [[no:Nålkapselmoser]] [[nn:Nålkapselmosar]] [[pl:Glewiki]] [[pt:Anthocerotophyta]] [[ru:Антоцеротовидные]] [[simple:Hornwort]] [[sk:Rožteky]] [[fi:Sarvisammalet]] [[sv:Nålfruktsmossor]] [[tl:Hornwort]] [[tr:Boynuz otları]] [[uk:Антоцеротовидні]] [[zh:角苔纲]]'