Common names
hornwort
Full scientific name

Ceratophyllum demersum L.

Number of records
1041
Currently classified as a weed
Yes

Hornwort (Ceratophyllum demersum) is a long-lived, submerged aquatic herb that is native to all continents except Antarctica. It was first recorded in the wild (naturalised) in New Zealand in 1961. The plant has long, freely branching stems with dark green leaves arranged in whorls. The leaves are repeatedly divided into narrow segments, giving them a bushy, horn-like appearance. It flowers from spring to autumn, producing tiny, inconspicuous flowers beneath the water surface, which develop into small, spiny fruits. It reproduces mainly vegetatively from stem fragments. Stem fragments are dispersed by water, boats, trailers, machinery and other human activities. Even small stem fragments readily produce new plants. It grows in still or slow-moving freshwater and can form dense underwater beds.

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