Any aquatic plant of the genus Ceratophyllum

• Forms submerged masses in ponds and slow-flowing streams
• Liverworts with slender hornlike 2-valved capsules

Wiktionary Word definitions in Wiktionary
n. A bryophyte with a leafless thallus characterized by a dominant gametophyte stage of the life cycle and a sporophyte stage shaped like a horn.

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Hornwort \Horn"wort`\, n. (Bot.) An aquatic plant ( Ceratophyllum ), with finely divided leaves.

WordNet Word definitions in WordNet
n. any aquatic plant of the genus Ceratophyllum; forms submerged masses in ponds and slow-flowing streams liverworts with slender hornlike 2-valved capsules

Wikipedia Word definitions in Wikipedia
Hornworts are a group of non-vascular plants comprising the division Anthocerotophyta . The common name refers to the elongated horn-like structure, which is the sporophyte . As in mosses and liverworts , the flattened, green plant body of a hornwort is ...