Hornwort - wikipedia Hornwort The name Hornwort also refers to aquatic plants of the genus Ceratophyllum, in the family Ceratophyllaceae Hornworts Temporal range : 90 -- 0 Ma PreЄ Є Pg Upper Cretaceous ( but see text ) to present Phaeoceros laevis ( L. ) Prosk. Scientific classification Kingdom : Plantae Division : Anthocerotophyta Stotler & Stotl. - Crand., 1977 Classes & Orders Leiosporocerotopsida Leiosporocerotales Anthocerotopsida Anthocerotales Dendrocerotales Notothyladales Phymatocerotales see Classification. Synonyms Anthocerotae Hornworts are a group of non-vascular plants constituting the division Anthocerotophyta. The common name refers to the elongated horn - like structure, which is the sporophyte. As in mosses and liverworts, 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. The total number of species is still uncertain. While there are more than 300 published species names, the actual number could be as low as 100 - 150 species. Contents 1 Description 2 Life cycle 3 Evolutionary history 4 Classification 4.1 Phylogeny 5 See also 6 References 7 External links Description The plant body of a hornwort is a haploid gametophyte stage. This stage usually grows as a thin rosette or ribbon - like thallus between one and five centimeters in diameter. Each cell of the thallus usually contains just one chloroplast. In most species, this chloroplast is fused with other organelles to form a large pyrenoid that both manufactures and stores food. This particular feature is very unusual in land plants, but is common among algae. 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 plants do. Unlike liverworts, most hornworts have true stomata on their sporophyte as mosses do. The exceptions are the genera Notothylas and Megaceros, which do not have stomata. The sporophyte of most hornworts are also photosynthetic, which is not the case with liverworts. When the sporophyte is mature, it has a multicellular outer layer, a central rod - like columella running up the center, and a layer of tissue in between that produces spores and pseudo-elaters. The pseudo-elaters are multi-cellular, unlike the elaters of liverworts. 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 bryophytes, measuring between 30 and 80 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 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. The tip of the germ tube divides to form an octant ( solid geometry ) 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. In either case, the protonema is a transitory stage in the life of a hornwort. 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 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 monoicous, with both sex organs on the same plant, but some plants ( even within the same species ) are dioicous, with separate male and female gametophytes. The female organs are known as archegonia ( singular archegonium ) and the male organs are known as 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 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 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 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 pseudo-elaters and spores. These are released from the capsule when it splits lengthwise from the tip. Evolutionary History This section needs expansion. You can help by adding to it. ( 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. 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 stomata. Classification The hornwort Dendroceros crispus growing on the bark of a tree. Hornworts were traditionally considered a class within the division Bryophyta ( bryophytes ). However, it now appears that this former division is paraphyletic, so the hornworts are now given their own division, Anthocerotophyta ( sometimes misspelled Anthocerophyta ). The division Bryophyta is now restricted to include only mosses. 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 orders, each containing a single 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 genera are a current matter of investigation, and several competing classification schemes have been published since 1988. Structural features that have been used in the classification of hornworts include : the anatomy of chloroplasts and their numbers within cells, the presence of a pyrenoid, the numbers of antheridia within androecia, and the arrangement of jacket cells of the antheridia. Phylogeny Recent studies of molecular, ultrastructural, and morphological data have yielded a new classification of hornworts. 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 ) Leiosporocerotaceae Leiosporoceros Anthocerotaceae Folioceros Sphaerosporoceros Anthoceros Notothyladaceae Notothylas Phaeoceros Phymatocerotaceae Phymatoceros Dendrocerotaceae Phaeomegaceros Nothoceros Megaceros Dendroceros The current phylogeny and composition of the Anthocerotophyta. See also Embryophyte References Jump up ^ Stotler, Raymond E. ; Barbara J. Candall - Stotler ( 1977 ). `` A checklist of the liverworts and hornworts of North America ''. The Bryologist. American Bryological and Lichenological Society. 80 ( 3 ) : 405 -- 428. doi : 10.2307 / 3242017. JSTOR 3242017. Jump up ^ What is a hornwort ? - Australian National Botanic Gardens Jump up ^ Mosses, Liverworts, and Hornworts ^ Jump up to : Chopra, R.N. ; Kumra, P.K. ( 1988 ). Biology of Bryophytes. New York : John Wiley & Sons. ISBN 0 - 470 - 21359 - 0. Jump up ^ Qiu, Y.L. ; Li, L. ; Wang, B. ; Chen, Z. ; Knoop, V. ; Groth - malonek, M. ; Dombrovska, O. ; Lee, J. ; Kent, L. ; Rest, J. ; et al. ( 2006 ). `` The deepest divergences in land plants inferred from phylogenomic evidence ''. Proceedings of the National Academy of Sciences. 103 ( 42 ) : 15511 -- 6. doi : 10.1073 / pnas. 0603335103. PMC 1622854. PMID 17030812. Jump up ^ Kenrick, Paul ; Peter R. Crane ( 1997 ). The Origin and Early Diversification of Land Plants : A Cladistic Study. Washington, D.C. : Smithsonian Institution Press. pp. 55 -- 56. ISBN 1 - 56098 - 730 - 8. Jump up ^ D. Christine Cargill, Karen S. Renzaglia, Juan Carlos Villarreal, and R. Joel Duff ( 2005 ), `` Generic concepts within hornworts : Historical review, contemporary insights and future directions '', Australian Systematic Botany, 18 : 7 -- 16, doi : 10.1071 / sb04012 CS1 maint : Uses authors parameter ( link ) ^ Jump up to : Duff, R. Joel ; Juan Carlos Villarreal ; D. Christine Cargill ; Karen S. Renzaglia ( 2007 ). `` Progress and challenges toward a phylogeny and classification of the hornworts ''. The Bryologist. 110 ( 2 ) : 214 -- 243. doi : 10.1639 / 0007 - 2745 ( 2007 ) 110 ( 214 : PACTDA ) 2.0.CO ; 2. Jump up ^ Villareal, J.C. ; Cargill, D.C. ; Hagborg, A. ; Söderström, L. ; Renzaglia, K.S. ( 2010 ). `` A synthesis of hornwort diversity : Patterns, causes and future work '' ( pdf ). Phytotaxa. 9 : 150 -- 166. Grolle, Riclef ( 1983 ). `` Nomina generica Hepaticarum ; references, types and synonymies ''. Acta Botanica Fennica. 121 : 1 -- 62. Hasegawa, J. ( 1994 ). `` New classification of Anthocerotae ''. Journal of the Hattori Botanical Laboratory. 76 : 21 -- 34. Renzaglia, Karen S. ( 1978 ). `` A comparative morphology and developmental anatomy of the Anthocerotophyta ''. Journal of the Hattori Botanical Laboratory. 44 : 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. 1 -- 20. Cambridge : Cambridge University Press. ISBN 0 - 521 - 66097 - 1. Schofield, W.B. ( 1985 ). Introduction to Bryology. New York : Macmillan. Schuster, Rudolf M. ( 1992 ). The Hepaticae and Anthocerotae of North America, East of the Hundredth Meridian. VI. Chicago : Field Museum of Natural History. Smith, Gilbert M. ( 1938 ). Cryptogamic Botany, Volume II : Bryophytes and Pteridophytes. New York : McGraw - Hill Book Company. Watson, E.V. ( 1971 ). The Structure and Life of Bryophytes ( 3rd ed. ). London : Hutchinson University Library. ISBN 0 - 09 - 109301 - 5. External links Wikimedia Commons has media related to Anthocerotophyta. Wikispecies has information related to Anthocerotophyta Hornwort Web Portal Anthocerotophyta description and fossil history at UCMP Classification of the Anthocerotophyta New Zealand Anthocerotae Classification of Archaeplastida / Plantae sensu lato Domain Archaea Bacteria Eukaryota ( Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta Animal Fungi ) Rhodophyta ( red algae ) Cyanidiophyceae Porphyridiophyceae Compsopogonophyceae Stylonematophyceae Rhodellophyceae Bangiophyceae Florideophyceae Glaucocystophyta ( glaucophytes ) Glaucocystophyceae Glaucocystis Cyanophora Gloeochaete Viridiplantae ( green algae, & land plants ) Mesostigmatophyceae Chlorokybophyceae C + S Chlorophyta Palmophyllales Nephrophyceae Prasinophyceae Pseudoscourfieldiales Pyramimonadophyceae Scourfieldiales Pedinophyceae Chlorodendrophyceae UTC clade Ulvophyceae Trebouxiophyceae Chlorophyceae Streptophyta ( charophytes, & land plants ) Klebsormidiophyceae Phragmo - plastophyta Charophyceae Coleochaetophyceae Zygnematophyceae Embryophyta ( land plants ) Bryophytes ( non-vascular ) Marchantiophyta Anthocerotophyta Bryophyta `` Moss '' † Horneophytopsida Tracheophyta ( vascular ) Lycopodiophyta ( microphylls ) † Zosterophyllopsida † Sawdoniales Isoetopsida Lycopodiopsida Euphyllophyta ( megaphylls ) Moniliformopses ( ferns ) † Cladoxylopsida † Stauropteridales † Zygopteridales Equisetopsida Psilotopsida Marattiopsida Polypodiopsida Spermatophyta ( seed plants ) † Seed ferns Gymnosperms Gnetopsida Pinopsida Cycadopsida Ginkgoopsida Angiosperms or flowering plants Amborellales Nymphaeales Austrobaileyales Magnoliids Monocots Eudicots Other † Trimerophytopsida † Progymnosperm Other † Rhyniopsida † = extinct. See also the list of plant orders. Taxon identifiers Wd : Q191156 EoL : 3678 EPPO : 1AHOP ITIS : 500000 NCBI : 13809 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Hornwort&oldid=826085828 '' Categories : Hornworts Bryophytes Turonian first appearances Extant Late Cretaceous first appearances Hidden categories : CS1 maint : Uses authors parameter Articles with ' species ' microformats Wikipedia articles needing clarification from August 2014 Articles to be expanded from June 2008 All articles to be expanded Articles using small message boxes Talk Contents About Wikipedia Wikispecies Afrikaans Azərbaycanca Беларуская Български Català Čeština Cymraeg Dansk Deutsch Eesti Español Esperanto Euskara فارسی Français 한국어 Hrvatski Bahasa Indonesia Interlingua Íslenska Italiano עברית Lietuvių Magyar Македонски മലയാളം Nederlands 日本 語 Nordfriisk Norsk Norsk nynorsk Polski Português Русский Simple English Slovenčina Srpskohrvatski / српскохрватски Suomi Svenska Tagalog ไทย Türkçe Українська Tiếng Việt Winaray 中文 38 more Edit links This page was last edited on 17 February 2018, at 03 : 13. 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Question: where does the sporophyte of a hornwort develop
Answer: from an archegonium