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{{Short description|Genus of aquatic plants}}
{{Redirect|Caulinia|the defunct legume genus ''Caulinia'' Moench|Kennedia}}
{{For|the non-profit organization|National Association of Japan-America Societies}}
{{Automatic taxobox
|image = Illustration Najas marina0.jpg
|image_caption = ''Najas marina''<ref>Otto Wilhelm Thomé. Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany</ref>
|taxon = Najas
|authority = [[Carl Linnaeus|L.]]
|synonyms_ref = <ref name=wet>[http://apps.kew.org/wcsp/synonomy.do?name_id=308218 Kew World Checklist of Selected Plant Families]</ref>
|synonyms = 
* ''Fluvialis'' <small>Ség</small>
* ''Caulinia'' <small>Willd.</small>
* ''Ittnera'' <small>C.C.Gmel.</small>
}}

'''''Najas''''', the '''water-nymphs'''<ref>{{PLANTS |id=NAJAS|taxon=Najas |accessdate=16 July 2015 }}</ref> or '''naiads''', is a [[genus]] of [[aquatic plant]]s. It is [[cosmopolitan (distribution)|cosmopolitan]] in distribution, first described for modern science by [[Carl Linnaeus|Linnaeus]] in 1753. Until 1997, it was rarely placed in the [[Hydrocharitaceae]],<ref name=tanaka>{{citation |doi=10.1007/BF02524931 |title=Phylogeny of the family hydrocharitaceae inferred fromrbcL andmatK gene sequence data |year=1997 |last1=Tanaka |first1=Norio |last2=Setoguchi |first2=Hiroaki |last3=Murata |first3=Jin |journal=Journal of Plant Research |volume=110 |issue=3 |pages=329–337 |bibcode=1997JPlR..110..329T |s2cid=10939773 }}</ref><ref name=les>{{citation |title=Phylogenetic studies in Alismatidae, II: Evolution of Marine Angiosperms (Seagrasses) and Hydrophily |year=1997 |last1=Les |first1=DH |last2=Cleland |first2=MA |last3=Waycott |first3=M |journal=Systematic Botany |volume=22 |issue=3 |pages=443 |doi=10.2307/2419820 |jstor=2419820 }}</ref><ref>[https://web.archive.org/web/20000712110354/http://www.ars-grin.gov/cgi-bin/npgs/html/gnlist.pl?561 Genera of Hydrocharitaceae], ''GRIN Taxonomy for Plants''</ref><ref name="apg2003">Angiosperm Phylogeny Group (2003). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II". ''Botanical Journal of the Linnean Society'' '''141'''(4): 399-436. (Available online: [https://archive.today/20120919163719/http://www3.interscience.wiley.com/journal/118872219/abstract Abstract] | [https://archive.today/20121205102805/http://www3.interscience.wiley.com/cgi-bin/fulltext/118872219/HTMLSTART Full text (HTML)] | [http://www3.interscience.wiley.com/cgi-bin/fulltext/118872219/PDFSTART Full text (PDF)]{{dead link|date=February 2019|bot=medic}}{{cbignore|bot=medic}})</ref> and was often taken as constituting (by itself) the family Najadaceae.<ref>[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10603 197. Najadaceae A. L. de Jussieu], ''[[Flora of North America]]''</ref>

The [[APG II system]], of 2003 (unchanged from the [[APG system]], of 1998), places the genus in family [[Hydrocharitaceae]], in the order [[Alismatales]] of the [[Monocotyledon|monocots]].<ref name="apg2003"/>

An infrageneric classification of two sections is proposed: Section ''Americanae'' and sect. ''Caulinia''.<ref name="Ito et al. 2017">Ito, Y., Nr. Tanaka, S.W. Gale, O. Yano, J. Li (2017) "Phylogeny of Najas (Hydrocharitaceae) revisited: Implications for systematics and evolution". ''Taxon'' '''66'''(2): 309-323. [https://doi.org/10.12705/662.2 doi: 10.12705/662.2]</ref>

;Species<ref name=wet/>
# ''[[Najas affinis]]'' <small>Rendle</small> - South America, Senegal, Guinea-Bissau
# ''[[Najas ancistrocarpa]]'' <small>A.Braun ex Magnus</small> - China, Japan, Taiwan
# ''[[Najas arguta]]'' <small>Kunth</small> - Cuba, Costa Rica, Panama, South America
# ''[[Najas australis]]'' <small>Bory ex Rendle</small> - India, Madagascar, Mauritius, KwaZulu-Natal, Seychelles
# ''[[Najas baldwinii]]'' <small>Horn</small> - West Africa
# ''[[Najas brevistyla]]'' <small>Rendle</small> - Assam
# ''[[Najas browniana]]'' <small>Rendle</small> - southern China, India, Taiwan, Java, Cavern Island in Northern Territory of Australia
# ''[[Najas chinensis]]'' <small>N.Z.Wang</small> - Primorye, China, Taiwan, Japan
# ''[[Najas conferta]]'' <small>(A.Braun) A.Braun</small> - Cuba, Hispaniola, Panama, Brazil
# ''[[Najas faveolata]]'' <small>A. Br. ex Magnus</small>
# ''[[Najas filifolia]]'' <small>R.R.Haynes</small> - southeastern United States (Georgia, Alabama, Florida)
# ''[[Najas flexilis]]'' <small>(Willd.) Rostk. & W.L.E. Schmidt</small> - temperate Northern Hemisphere
# ''[[Najas gracillima]]'' (A.Braun ex Engelm.) Magnus - Asia, North America
# ''[[Najas graminea]]'' <small>Delile</small> - Africa, Asia, New Guinea, Melanesia, northern Australia; naturalized in California and parts of Europe
# ''[[Najas grossareolata]]'' <small>L.Triest</small> - Sri Lanka
# ''[[Najas guadalupensis]]'' <small>(Spreng.) Magnus</small> - North and South America, Caribbean
# ''[[Najas hagerupii]]'' <small>Horn</small> - Ghana, Mali
# ''[[Najas halophila]]'' <small>L.Triest</small> - Java, New Guinea, Queensland
# ''[[Najas heteromorpha]]'' <small>Griff. ex Voigt</small> - eastern India
# ''[[Najas horrida]]'' <small>A.Braun ex Magnus</small> - Africa, Madagascar, Sinai
# ''[[Najas indica]]'' <small>(Willd.) Cham.</small> - Indian Subcontinent, China, Southeast Asia, New Guinea
# ''[[Najas kurziana ]]'' <small>Rendle</small> - Bihar, East Timor
# ''[[Najas madagascariensis]]'' <small>Rendle</small> - Madagascar; naturalized in Mauritius
# ''[[Najas malesiana]]'' <small>W.J.de Wilde</small> - India, Bangladesh, Indochina, Malaysia, Indonesia, Philippines; naturalized in eastern Brazil
# ''[[Najas marina]]'' <small>L.</small> - widespread and nearly cosmopolitan
# ''[[Najas minor]]'' <small>All.</small> - widespread in Europe, Asia, Africa; naturalized in eastern North America
# ''[[Najas oguraensis]]'' <small>Miki</small> - East Asia, Himalayas (Pakistan, Nepal, northern India)
# ''[[Najas pectinata]]'' <small>(Parl.) Magnus</small> - Sahara
# ''[[Najas pseudogracillima]]'' <small>L.Triest</small> - Hong Kong
# ''[[Najas rigida]]'' <small>Griff.</small> - eastern India
# ''[[Najas schweinfurthii]]'' <small>Magnus</small> - Senegal, Cameroon, Ethiopia, Sudan, Tanzania 
# ''[[Najas tenuicaulis]]'' <small>Miki</small> - Honshu Island in Japan
# ''[[Najas tenuifolia]]'' <small>R.Br.</small> - Hong Kong, Southeast Asia, Australia
# ''[[Najas tenuis]]'' <small>Magnus</small> – India, Sri Lanka, Myanmar
# ''[[Najas tenuissima]]'' <small>(A.Braun ex Magnus) Magnus</small> - Finland, Russia, Hokkaido
# ''[[Najas testui]]'' <small>Rendle</small> - western + central Africa
# ''[[Najas welwitschii]]'' <small>Rendle</small> - tropical Africa, western India
# ''[[Najas wrightiana]]'' <small>A.Braun</small> - Mexico, Central America, Cuba, Bahamas, Venezuela; naturalized in Florida

==References==
{{Reflist}}

==External links==
* [http://delta-intkey.com/angio/www/najadace.htm Najadaceae] {{Webarchive|url=https://web.archive.org/web/20090201131049/http://delta-intkey.com/angio/www/najadace.htm |date=2009-02-01 }} in L. Watson and M.J. Dallwitz (1992 onwards) [http://delta-intkey.com/angio/ ''The families of flowering plants''] {{Webarchive|url=https://web.archive.org/web/20070103200438/http://delta-intkey.com/angio/ |date=2007-01-03 }}: descriptions, illustrations, identification, information retrieval. Version: 9 March 2006. http://delta-intkey.com {{Webarchive|url=https://web.archive.org/web/20070103200438/http://delta-intkey.com/ |date=2007-01-03 }}.
* [http://www.alpine-plants-jp.com/art/itotorigemo_1.htm ''Najas japonica'' Nakai]- Flavon's art gallery
* [http://greif.uni-greifswald.de/floragreif/?fam=Najadaceae&gen=&spec=&flora_search=taxon Najadaceae of Mongolia in FloraGREIF]

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[[Category:Najas| ]]
[[Category:Aquatic plants]]
[[Category:Hydrocharitaceae genera]]
[[Category:Taxa named by Carl Linnaeus]]