Description:

• Submerged, fern-like, annual or rarely perennial herbs found on rocks in fast-flowing freshwater, dioecious or rarely monoecious; rhizome discoid or tuberous, forming a compact circle of roots, firmly attached to rocks
• Leaves basal, 2- or 3-pinnatifid, petiolate, dilated and ligulate at base, petiole and rachis densely covered with warty to tongue-shaped protuberances; pinnae dissected into multifid, variously-shaped outgrowths ('gill-tufts')
• Inflorescence emergent, densely spicate (resembling fruiting spikes of Plantago major); scape verrucose or rarely smooth
• Flowers unisexual, small, sessile, solitary in axils of spirally arranged, closely imbricate bracts; calyx and corolla 0
• Male flowers consisting of one sessile or subsessile stamen with 2 oblong thecae; pollen in tetrads, copious
• Female flowers: ovary superior, of 2 fused carpels, 1-locular, many-ovuled, with 2 parietal placentas; styles 2, exserted from the bracts, persistent
• Fruit a 2-valved capsule, enclosed in persistent bract
• Seeds small, light, many; endosperm 0

Nomenclature:

• Hydrostachys Thouars
  • Thouars: 2 (1806)
  • Obermeyer: 211 (1970)
  • Cusset: 75 (1973)
  • Cook: 105 (1990)
  • Stannard 10 (1997)

Distribution & Notes:

• Global: Species 22
• Southern Africa: Species 1: Hydrostachys polymorpha Klotzsch, a fragmentary distribution, in rapids in the Kunene River in Namibia and in the Umgeni and Umkomaas Rivers in KwaZulu-Natal