Ceratophyllum submersum

Tracheophyta MagnoliopsidaCeratophyllaceaeCeratophyllumCeratophyllum submersum

Ecology

This aquatic grows in eutrophic or slightly brackish water in shallow, sheltered lakes, ponds and ditches. It is particularly frequent in coastal grazing marshes. Like C. demersum, reproduction is mostly by vegetative fragmentation and it can occur in dense masses, even in shaded ponds. Lowland.

Status

Native

World Distribution

Eurosiberian Temperate element.

Broad Habitats

Standing water and canals

Light (Ellenberg): 7

Moisture (Ellenberg): 12

Reaction (Ellenberg): 8

Nitrogen (Ellenberg): 8

Salt Tolerance (Ellenberg): 2

January Mean Temperature (Celsius): 3.9

July Mean Temperature (Celsius): 16.3

Annual Precipitation (mm): 705

Length: 100

Perennation - primary

Perennial

Life Form - primary

Perennial hydrophyte (perennial water plant)

Woodiness

Herbaceous

Clonality - primary

Irregularly fragmenting (mainly water plants)

Count of 10km squares in Great Britain: 208

Count of 10km squares in Ireland: 3

Count of 10km squares in the Channel Isles: 5

Atlas Change Index: 0.39

JNCC Designations

NBNSYS0000002762

Scarce Atlas Account

Scarce Atlas Account: 

Ceratophyllum submersum L.        

Soft hornwort

Status: not scarce

 

 

This is a perennial aquatic plant of shallow, sheltered, eutrophic waters. It is one of the few British vascular plants which lack roots, growing as a floating mass or lightly anchored to the substrate by buried sterns. In coastal sites its most characteristic habitats are shallow ponds and ditches (including grazing marsh ditches), where it grows with other plants which tolerate slightly brackish conditions such as Myriophyllum spicatum, Potamogeton pectinatus, Ranunculus baudotii and Zannichellia palustris, as well as species of wider habitat range. At inland localities it grows in similar habitats to the commoner C. demersum, including small field ponds, lakes and flooded gravel pits. It is shade-tolerant, and can be found in ditches or small ponds surrounded by tall emergents. In both coastal and inland sites it can be so abundant that it virtually excludes all competitors. It is confined to the lowlands. 

Plants flower freely but mature fruit is less frequent (C. demersum is known to require high temperatures for the maturation of its fruit). Vegetative reproduction is probably frequent as plants are brittle and are able to regenerate from fragments. Plants survive the winter as sunken sterns, but are unable to tolerate prolonged freezing.

The simple vegetative distinction between C. submersum and C. demersum was not understood until 1927 (Sandwith 1927). Older records of C. submersum are unreliable, and have been accepted only if supported by herbarium specimens. It is therefore difficult to assess changes in the distribution of the species. C. submersum is being recorded with increasing frequency in inland sites, but it is not clear if this reflects a real increase or whether it was previously overlooked. As a species of eutrophic water, it is unlikely to be threatened by changes in water quality.

C. submersum sensu lato is widespread in Europe, north to southern Scandinavia (Jalas & Suominen 1989). It is also found in Asia, Africa and North and South America, but it is absent from Australasia. For a map of its world distribution, see Wilmot-Dear (1985).

 

 

C. D. Preston

Atlas text references

Atlas (28b)
Hultén E, Fries M
1986.  Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
Jalas & Suominen (1989)
Preston CD, Croft JM
1997.  Aquatic plants in Britain and Ireland.
Stewart A, Pearman DA, Preston CD
1994.  Scarce plants in Britain.