Ceratophyllum demersum aka Common Hornwort

Ceratophyllum demersum is also known as hornwort. It belongs to the family Ceratophyllaceae. Other names are coon tail, cedar moss and rigid hornwort. Kew lists its native range as worldwide. The RHS confirms it is native to Britain and Ireland. It grows in ponds and ditches, including in temperate zones. It lives in water, not as a dry-ground perennial. PFAF calls it perennial, meaning it lives for years. Kew also records annual and subshrub forms that live in water.

Hornwort grows fast to about 3.3 feet [1 metre]. Most growth stays below water, but it may float on top. It serves as a pond oxygenator through its growth underwater. A pond suits it better than a normal garden bed. It can grow in sun or part shade. PFAF says it copes with shade better than many underwater plants. Yet it prefers full sun when grown in gardens.

PFAF gives its bloom time as July to September. Each plant has male flowers and separate female flowers. Water moves pollen from one to the other. Male anthers break free and rise to the surface. These pollen-bearing parts then let their pollen go. The pollen sinks and reaches the female flowers below water. Thus, the plant can pollinate without insects or wind. But it more often makes new plants without seeds. You can take cuttings during the growing season. PFAF says these take root with ease.

PFAF lists sand, loam and clay as fit growing media. The plant prefers sand enriched with decayed organic matter. Its stated pH range is mildly acid to mildly alkaline. It needs wet ground, in keeping with life in water. PFAF gives USDA hardiness zones of 7–10. Bear its need for water in mind when choosing a site. A soil label alone does not tell you all it needs.

PFAF lists the leaves as edible but gives a low food-use rating. It gives no details on how to prepare or serve them. PFAF also reports no known hazards. This does not prove safety for each person or pet. It records past medicinal uses for fevers that recur and scorpion stings. These records do not prove that such treatments work. The supplied facts best support its garden use underwater in ponds.