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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.