Common names: hornwort, coontail

Family: Ceratophyllaceae

Could be confused with: Aldrovanda, Cabomba, Chara, Hippuris, Hydrotriche, Myriophyllum.

Native distribution: Cosmopolitan.

Species commonly cultivated:
Ceratophyllum demersum L. (worldwide)
C. submersum L. (worldwide)

Adventive distribution: Difficult to ascertain.

Weed status: Sometimes troublesome in lakes and rivers (rarely a persistent problem).

Habit: Submersed, rootless, branching stem plant.

Brief description: Perennial. Submersed, rootless, highly branched; shoots often brittle; shoot apices sometimes modified as resting stage 'rhizoids.' Leaves arranged in evenly spaced whorls of 6-12, more densely spaced and usually curved upwards towards growing tip, sessile, dichotomously dissected into filiform segments, dissection branching pattern variable; margin with minute serrations or teeth. Inflorescence small, axillary, solitary or grouped, sessile or shortly pedicellate. Flowers unisexual, with male and female flowers on different leaf nodes; perianth of 8-12 segments. Dispersal by seed, 'rhizoids' or stem fragments.

Natural habitat: Still water of lakes, rivers, ponds, and swamps.

Additional comments: Ceratophyllum contains at least four, highly variable species. This variability has led to numerous species, subspecies and varieties being erected from different geographic regions. Ceratophyllum often remains persistent in water bodies in the presence of highly invasive weeds that may have displaced other native species. May undergo an annual cycle of sinking and partial decay of old stems in winter, and then rising to just below surface in spring as new growth starts.