demersum

Rigid Hornwort or Common Hornwort

Cosmopolitan.


muricatum

Prickly Hornwort

Widespread in many places though not all countries


platyacanthum

Scattered locations in Germany, Hungary, France, Russia, China, Japan, Korea


submersum

Soft Hornwort or Tropical Hornwort

Europe, Central Asia, northern Africa, scattered places in tropical Africa, Turkey, Oman, Florida, Dominican Republic


tanaiticum

Endemic to Hungary and eastern Europe.