Hydrostachys

Hydrostachys is a genus of about 22 species^[2] 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 pinnately compound leaves, and highly reduced flowers on dense spikes.^[3]

Hydrostachys
Hydrostachys imbricata
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Cornales
Family:	Hydrostachyaceae Engl.[1]
Genus:	Hydrostachys Thouars
Species
Approximately 22; see text.

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.^[3][4] Its position in Cornales is uncertain; it may be basal to the rest of the order, or it may fall within the family Hydrangeaceae.^[3][5][6] It shares few morphological similarities with other Cornales.^[3]

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