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””’Hydrostachys””’ is a genus of about 22 species<ref name=”Christenhusz-Byng2016″>{{cite journal |author1=Christenhusz, M. J. M. |author2=Byng, J. W. | year = 2016 | title = The number of known plants species in the world and its annual increase | journal = Phytotaxa | volume = 261 | pages = 201–217 | url = http://biotaxa.org/Phytotaxa/article/download/phytotaxa.261.3.1/20598 | doi = 10.11646/phytotaxa.261.3.1 | issue = 3 | doi-access = free }}</ref> of [[flowering plant]]s native to [[Madagascar]] and southern and central [[Africa]]. It is the only genus in the family ”’Hydrostachyaceae”’. All species of ”Hydrostachys” are aquatic, growing on rocks in fast-moving water. They have tuberous roots, usually [[Leaf#Divisions of the lamina .28blade.29|pinnately compound]] leaves, and highly reduced flowers on dense spikes.<ref name=Albach2001>Albach, D. C., Soltis, D. E., Chase, M. W., and [[Soltis, P. S.]] (2001). Phylogenetic placement of the enigmatic angiosperm ”Hydrostachys”. Taxon 50, 781-805.</ref>
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””’Hydrostachys””’ is a genus of about 22 species<ref name=”Christenhusz-Byng2016″>{{cite journal |author1=Christenhusz, M. J. M. |author2=Byng, J. W. | year = 2016 | title = The number of known plants species in the world and its annual increase | journal = Phytotaxa | volume = 261 | pages = 201–217 | url = http://biotaxa.org/Phytotaxa/article/download/phytotaxa.261.3.1/20598 | doi = 10.11646/phytotaxa.261.3.1 | issue = 3 | doi-access = free }}</ref> of [[flowering plant]]s native to [[Madagascar]] and southern and central [[Africa]]. It is the only genus in the family ”’Hydrostachyaceae”’. All species of ”Hydrostachys” are aquatic, growing on rocks in fast-moving water. They have tuberous roots, usually [[Leaf#Divisions of the lamina .28blade.29|pinnately compound]] leaves, and highly reduced flowers on dense spikes.<ref name=Albach2001>Albach, D. C., Soltis, D. E., Chase, M. W., and [[Soltis, P. S.]] (2001). Phylogenetic placement of the enigmatic angiosperm ”Hydrostachys”. Taxon 50, 781-805.</ref>
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[[Phylogenetic]] placement of ”Hydrostachys” is particularly problematic.
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[[Phylogenetic]] placement of ”Hydrostachys” is particularly problematic. to its specialized aquatic morphology, it has often been grouped with other aquatic plants, such as the family [[Podostemaceae]]. However, embryological, floral, and other morphological characters do not support this placement, and molecular data suggest that ”Hydrostachys” is related to taxa in the order [[Cornales]].<ref name=Albach2001 /><ref name=APGIV>{{Cite journal|author=Angiosperm Phylogeny Group |author-link=Angiosperm Phylogeny Group|year=2016|title=An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV|journal=[[Botanical Journal of the Linnean Society]]|volume=181|issue=1|pages=1–20|issn=0024-4074|doi=10.1111/boj.12385|doi-access=free}}</ref> Its position Cornales uncertain; it may be basal to the rest of the order or may fall within the family [[Hydrangeaceae]].<ref name=Albach2001 /><ref name=Fan2003>Fan, C. Z., and Xiang, Q. Y. (2003). Phylogenetic analyses of Cornales based on 26S rRNA and combined 26S rDNA-matK-rbcL sequence data. ”American Journal of Botany” ”’90”’, 1357-1372.</ref><ref name=Kubitzki2004>Kubitzki, K. (2004). Cornaceae. In ”The Families and Genera of Vascular Plants Volume 6: Flowering Plants: Dicotyledons: Celastrales, Oxidales, Rosales, Cornales, Ericales” (Kubitzki, ed.). Springer-Verlag, New York.</ref> It shares few morphological similarities with other Cornales.<ref name=Albach2001 />
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==Species==
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==Species==
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Hydrostachys
