hornwort
noun
horn·wort ˈhȯrn-ˌwərt 
-ˌwȯrt
: any of a genus (Ceratophyllum of the family Ceratophyllaceae) of rootless thin-stemmed aquatic monoecious herbs with female flowers having a single carpel
Example Sentences
Recent Examples on the Web Anthocerotae Anthocerotae, also known as hornworts, are the third type of bryophyte. 
Kevin Espiritu For Partselect.com, Good Housekeeping, 29 Aug. 2017 Oishi said humid cities where moss thrives could benefit most from using bryophytes – a collective term for mosses, hornworts and liverworts – as bioindicators, adding moss could be monitored in its natural environment or cultivated for analysis. Sophie Hares, The Christian Science Monitor, 21 Aug. 2017
Kevin Espiritu For Partselect.com, Good Housekeeping, 29 Aug. 2017 Oishi said humid cities where moss thrives could benefit most from using bryophytes – a collective term for mosses, hornworts and liverworts – as bioindicators, adding moss could be monitored in its natural environment or cultivated for analysis. Sophie Hares, The Christian Science Monitor, 21 Aug. 2017 Word History
First Known Use
circa 1805, in the meaning defined above