Rigid Hornwort

Rigid Hornwort - Ceratophyllum demersum

Submerged waterweed with very thin (0,5 mm), flexible, but strong stem growing up to two metres in length; branched, rootless, either free floating or anchored at the bottom by means of colourless shoots.

Rigid but brittle dark green leaves in whorls, bifurcated once or twice, toothed and prickly along outer edge. Separate, small, insignificant male and female flowers, but both carried on the same branch at the leaf axil.

The Rigid Hornwort flowers from June to August, pollination is by water. The plant propagates mostly by vegetative reproduction, and under adverse meteorological conditions by over-wintering buds (hibernaculi).

This species lives in stagnant or slow-flowing waters, rich in nutrients and sometimes slightly eutrophic, which tend to warm up in summer. C. demersum is often associated with water-lilies and pondweeds.

Reclamation in the form of canalisation and draining have drastically cut down the occurrence of the waterweed, once widespread and very common in the inland waters of northern Italy and Tuscany but rather rare.