One of the three Divisions of bryophytic plants
Ceratophyllum, in the family Ceratophyllaceae The name Hornwort besides refers to aquatic plants of the genus, in the class Ceratophyllaceae
Hornworts are a group of bryophytes ( a group of non-vascular plants ) constituting the division Anthocerotophyta ( ). The park list refers to the elongated horn-like social organization, which is the sporophyte. As in mosses and liverworts, the flattened, green plant body of a hornwort is the gametophyte implant.

Hornworts may be found global, though they tend to grow entirely in places that are damp or humid. Some species grow in bombastic numbers as bantam weeds in the dirty of gardens and cultivated fields. Large tropical and sub-tropical species of Dendroceros may be found growing on the bark of trees. The full count of species is still uncertain. While there are more than 300 print species names, the actual number could be equally abject as 100-150 species. [ 2 ]

description [edit ]

The plant body of a hornwort is a haploid gametophyte degree. This stage normally grows as a thinly rosette or ribbon-like thallus between one and five centimeters in diameter. Each cell of the thallus normally contains equitable one chloroplast. In half of the roughly 200 hornwort species, this chloroplast is fused with early organelles to form a big pyrenoid that both enables more effective photosynthesis and stores food. The pyrenoid is comprised predominantly of RuBisCO, the key enzyme in carbon fixation. By using inorganic carbon paper transporters and carbonaceous anhydrases, astir to a 50-fold increase in CO2 levels can be achieved. [ 3 ] This particular feature is very unusual in kingdom plants, singular to hornworts, but is coarse among alga. [ 4 ] [ 5 ] many hornworts develop internal glue -filled cavities or canals when groups of cells break down. They will secrete hormogonium-inducing factors ( HIF ) that stimulate nearby, free-living photosynthetic cyanobacteria, particularly species of Nostoc, to invade and colonize these cavities. [ 6 ] such colonies of bacteria growing inside the thallus give the hornwort a classifiable bluish green color. There may besides be little slime pores on the bottom of the thallus. These pores superficially resemble the stoma 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, alternatively of from its point the way other plants do. Unlike liverworts, most hornworts have true stomata on their sporophyte as mosses do. The exceptions are the genus Notothylas and Megaceros, which do not have stomata. The sporophyte of most hornworts are besides photosynthetic, which is not the case with liverworts. [ 7 ] The sporophyte lacks an apical meristem, an auxin -sensitive decimal point of deviation with early kingdom plants some time in the Late Silurian / Early Devonian. [ 8 ] [ 9 ] 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 coiling 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, normally with a distinctive y-shaped tri-radiate ridge on the proximal airfoil, and with a distal surface ornamented with bumps or spines

Life cycle [edit ]

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. [ 10 ] The tap of the microbe tube divides to form an octant ( solid geometry ) of cells, and the beginning rhizoid grows as an extension of the original source cell. [ clarification needed ] The tip continues to divide newfangled cells, which produces a thalloid protonema. By line, species of the family Dendrocerotaceae may begin dividing within the spore, becoming multicellular and even photosynthetic before the spore germinates. [ 10 ] In either event, the protonema is a ephemeral stage in the life of a hornwort .
Phaeoceros. Click on the image to enlarge. Life cycle of a typical hornwort. Click on the picture to enlarge. From the protonema grows the adult gametophyte, which is the persistent and freelancer degree in the life cycle. This stage normally 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 arouse organs of the hornwort. Most plants are monoecious, with both sex organs on the same plant, but some plants ( even within the same species ) are dioecious, with separate male and female gametophytes. The female organs are known as archegonium ( curious archegonium ) and the male organs are known as antheridium ( singular antheridium ). Both kinds of organs develop just below the come on of the plant and are entirely subsequently exposed by decay of the overlying cells. The biflagellate sperm must swim from the antheridium, or else be splashed to the archegonium. When this happens, the sperm and egg cell fuse to form a zygote, the cell from which the sporophyte phase of the biography motorbike will develop. Unlike all early bryophytes, the beginning cellular telephone division of the zygote is longitudinal. further divisions produce three basic regions of the sporophyte. At the bottom of the sporophyte ( closest to the inside of the gametophyte ), is a infantry. This is a ball-shaped group of cells that receives nutrients from the rear gametophyte, on which the sporophyte will spend its entire being. In the in-between of the sporophyte ( good above the foot ), is a meristem that will continue to divide and produce new cells for the third area. This third region is the condensation. Both the central and coat cells of the condensation are sterile, but between them is a layer of cells that will divide to produce pseudo-elaters and spores. These are released from the condensation when it splits lengthwise from the tiptoe .

evolutionary history [edit ]

While the fossil record of pennant 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 cardinal columella not attached at the roof. [ 11 ] however, the same form of columella is besides 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. [ 12 ] even if the cleave between hornworts and the other bryophytes happened much earlier, it is estimated that the last park ancestor of contemporary hornworts lived in middle permian about 275 million years ago. [ 13 ] Chromosome-scale genome sequence of three hornwort species corroborate that stoma evolved lone once during estate establish evolution. It besides shows that the three groups of bryophytes share a common ancestor that branched off from the early landplants early in evolution, and that liverworts and mosses are more closely related to each other than with hornworts. [ 14 ] Hornworts are alone in having a gene called LCIB, which is not found in any other know land plants but occurs in some species of alga. It allows them to concentrate carbon dioxide inside their chloroplasts, making the production of carbohydrate more effective. [ 15 ]

classification [edit ]

Dendroceros crispus growing on the bark of a tree. The hornwortgrowing on the bark of a tree. Hornworts were traditionally considered a class within the division Bryophyta ( bryophytes ). Later on, the bryophytes were considered paraphyletic, and hence the hornworts were given their own division, Anthocerotophyta ( sometimes misspelled Anthocerophyta ). however, the most recent phylogenetic attest leans strongly towards bryophyte monophyly, [ 16 ] [ 17 ] [ 18 ] [ 19 ] [ 20 ] [ 21 ] [ 22 ] [ 23 ] [ 24 ] [ excessive citations ] and it has been proposed that hornworts are de-ranked to the original classify Anthocerotopsida. [ 18 ] traditionally, there was a single class of hornworts, called Anthocerotopsida, or older Anthocerotae. More recently, a second class Leiosporocertotopsida has been segregated for the singularly strange species Leiosporoceros dussii. All other hornworts remain in the class Anthocerotopsida. These two classes are divided further into five orders, each containing a individual family. Among land plants, hornworts are one of the earliest-diverging lineages of the early land plant ancestors ; [ 14 ] cladistic analysis implies that the group originated anterior to the Devonian, around the same time as the mosses and liverworts. There are about 200 species known, but new species are silent being discovered. The number and names of genus are a stream matter of probe, and several competing categorization schemes have been published since 1988. morphologic features that have been used in the classification of hornworts include : the anatomy of chloroplasts and their numbers within cells, the bearing of a pyrenoid, the numbers of antheridium within androecium, and the placement of jacket cells of the antheridium. [ 25 ]

evolution [edit ]

recent studies of molecular, ultrastructural, and morphologic data have yielded a raw classification of hornworts. [ 26 ]

order Leiosporocerotales

Leiosporocerotaceae

  • Leiosporoceros (1 species)

order Anthocerotales

Anthocerotaceae

  • Anthoceros (ca. 83 species)
  • Folioceros (17 species)
  • Sphaerosporoceros (2 species)

rate 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)

arrange Dendrocerotales

Read more: Willem Dafoe

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.[26][27]

See besides [edit ]

References [edit ]

  • 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 BryophytesISBN 0-09-109301-5.