Ceratophyllum
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2008-07-09T01:51:44Z
EncycloPetey
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{{Taxobox
| name = ''Ceratophyllum''
| image = CeratophyllumSubmersum.jpg
| image_width = 250px
| image_caption = ''Ceratophyllum submersum''
| regnum = [[Plant]]ae
| divisio = [[Angiospermae]]
| classis = ''see text''
| ordo = '''Ceratophyllales'''
| ordo_authority = [[Gottlieb Wilhelm Bischoff|Bisch.]]
| familia = '''Ceratophyllaceae'''
| familia_authority = [[Samuel Frederick Gray|Gray]]
| genus = '''''Ceratophyllum'''''
| genus_authority = [[Carolus Linnaeus|L.]]
| subdivision_ranks = Species
| subdivision = See text
}}
'''''Ceratophyllum''''' is a [[cosmopolitan genus]] of [[flowering plant]]s, commonly found in ponds, marshes, and quiet streams in tropical and in temperate regions. They are usually called '''hornworts''', although this name is also used for unrelated plants of the division [[Anthocerotophyta]].
''Ceratophyllum'' grows completely submerged, usually, though not always, floating on the surface, and does not tolerate drought. The plant stems can reach 1–3 m in length. At intervals along nodes of the stem they produce rings of bright green [[leaf|leaves]], which are narrow and often much-branched. The forked leaves are brittle and stiff to the touch in some species, softer in others. The plants have no roots at all, but sometimes they develop modified leaves with a rootlike appearance, which anchor the plant to the bottom. The [[flower]]s are small and inconspicuous, with the male and female flowers on the same plant. In ponds it forms thick buds in the autumn that sink to the bottom which give the impression that it has been killed by the frost but come spring these will grow back into the long stems slowly filling up the pond.<ref name=foc>Flora of China: [http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=106192 ''Ceratophyllum'']</ref><ref name=fna>Flora of North America: [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=106192 ''Ceratophyllum'']</ref><ref name=blamey>Blamey, M. & Grey-Wilson, C. (1989). ''Flora of Britain and Northern Europe''. ISBN 0-340-40170-2</ref><ref name=rhs>Huxley, A., ed. (1992). ''New RHS Dictionary of Gardening''. Macmillan ISBN 0-333-47494-5.</ref>
Hornwort plants float in great numbers just under the surface. They offer excellent protection to fish-spawn, but also to snails, infected with [[bilharzia]]. Because of their appearance and their high oxygen production, they are often used in freshwater [[aquarium|aquaria]].
==Relationships and classification==
''Ceratophyllum'' is considered unique enough to warrant its own family, Ceratophyllaceae, and its precise relationship to other [[angiosperm]]s remains unclear. It was considered a relative of [[Nymphaeaceae]] and included in [[Nymphaeales]] in the [[Cronquist system]] but recent research has shown that it is not closely related to Nymphaeaceae or any other extant plant family. Some early molecular phylogenies suggested it was the [[sister group]] to all other angiosperms, but more recent ones have suggested that it is the sister group to either the [[monocots]] or the [[eudicots]]. The [[APG II]] system places the family in its own order, the Ceratophyllales.<ref name=mobot>Angiosperm Phylogeny Web: [http://www.mobot.org/MOBOT/Research/APweb/orders/ceratophyllalesweb.htm#Ceratophyllales Ceratophyllales]</ref>
The current phylogeny is:
{{clade| style=font-size:75%;line-height:75%
|label1=[[Angiospermae]]
|1={{clade
|1=''[[Amborella]]''
|2=[[Nymphaeaceae]]
|3=[[Austrobaileyales]]
|4={{clade
|label1=Mesangiospermae
|1={{clade
|1=[[Chloranthaceae]]
|2=[[magnoliids]]
|3='''''Ceratophyllum'''''
|4=[[monocots]]
|5=[[eudicots]]
}}
}}
}}
}}
The division of the genus into species is not completely settled. More than 30 species have been described, but many are probably just variants of these more widely accepted species:<ref name=grin>Germplasm Resources Information Network: [http://www.ars-grin.gov/cgi-bin/npgs/html/splist.pl?2302 ''Ceratophyllum'']</ref><ref name=apni>Australian Plant Name Index: [http://www.anbg.gov.au/cgi-bin/apni?taxon_name=Ceratophyllum%25 ''Ceratophyllum'']</ref><ref name=foc/><ref name=fe>Flora Europaea: [http://rbg-web2.rbge.org.uk/cgi-bin/nph-readbtree.pl/feout?FAMILY_XREF=&GENUS_XREF=Ceratophyllum&SPECIES_XREF=&TAXON_NAME_XREF=&RANK= ''Ceratophyllum'']</ref><ref name=fna/>
*''[[Ceratophyllum demersum]]'' L. (Rigid Hornwort or Common Hornwort)
*''[[Ceratophyllum echinatum]]'' A.Gray (Spineless Hornwort)
*''[[Ceratophyllum muricatum]]'' Cham. (Prickly Hornwort)
*''[[Ceratophyllum platyacanthum]]'' Cham.
*''[[Ceratophyllum submersum]]'' L. (Soft Hornwort or Tropical Hornwort)
Of these, ''Ceratophyllum demersum'' is widespread, with a global distribution; the others all have more restricted ranges.
==References==
{{reflist}}
<gallery>
Image:Ceratophyllum demersum2.gif|''Ceratophyllum demersum''
Image:Ceratophyllum demersum3.jpg|''Ceratophyllum demersum''
</gallery>
[[Category:Angiosperms]]
[[Category:Aquatic plants]]
[[Category:Plant families]]
[[ca:Ceratofil·lal]]
[[da:Hornblad]]
[[de:Hornblatt]]
[[es:Ceratophyllaceae]]
[[fr:Ceratophyllaceae]]
[[hsb:Drapaty rohačk]]
[[lv:Raglapes]]
[[lt:Nertiniai]]
[[hu:Ceratophyllales]]
[[nl:Ceratophyllales]]
[[ja:マツモ科]]
[[no:Hornblader]]
[[pl:Rogatek (roślina)]]
[[pt:Ceratophyllum]]
[[sr:Ceratophyllales]]
[[sv:Särvar]]
[[vi:Họ Rong đuôi chồn]]
[[zh:金鱼藻科]]
[[ru:Роголистник]]