''Hydrostachys'' is a genus of about 22 species
of flowering plants 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.
[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.]
Phylogenetic placement of ''Hydrostachys'' is particularly problematic. Due 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.
Its position in Cornales is uncertain; it may be basal to the rest of the order, or it may fall within the family Hydrangeaceae.
[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.][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.] It shares few morphological similarities with other Cornales.
Species
(This list may be incomplete.)
* ''Hydrostachys decaryi''
* ''Hydrostachys distichophylla''
* ''Hydrostachys fimbriata''
* ''Hydrostachys imbricata''
* ''Hydrostachys laciniata''
* ''Hydrostachys longifida''
* ''Hydrostachys maxima''
* ''Hydrostachys monoica''
* ''Hydrostachys multifida''
* ''Hydrostachys perrieri''
* ''Hydrostachys plumosa''
* ''Hydrostachys stolonifera''
* ''Hydrostachys trifaria''
* ''Hydrostachys verruculosa''
References
External links
''Hydrostachys'' on eFloras.org
{{Taxonbar, from1=Q285630, from2=Q1136814
Hydrostachyaceae
Cornales genera
Taxa named by Adolf Engler