''Ceratophyllum demersum'', commonly known as hornwort, rigid hornwort, coontail, or coon's tail, is a species of ''

Ceratophyllum ''Ceratophyllum'' is a cosmopolitan genus of flowering plants including four accepted living species in 2016, commonly found in ponds, marshes, and quiet streams in tropical and in temperate regions. It is the only extant genus in the family C ...

''. It is a submerged, free-floating

aquatic plant Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that g ...

, with a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

, native to all continents except Antarctica. It is a harmful introduced weed in New Zealand.Ceratophyllum demersum
on the Global Invasive Species database (2006). It is also a popular aquarium plant.

Description

An aquatic plant, ''Ceratophyllum demersum'' has stems that reach lengths of , with numerous side shoots making a single specimen appear as a large, bushy mass. The

leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...

are produced in whorls of six to twelve, each leaf 8–40 mm long, simple, or forked into two to eight thread-like segments edged with spiny teeth; they are stiff and brittle. It is monoecious, with separate male and female flowers produced on the same plant. The flowers are small, 2 mm long, with eight or more greenish-brown petals; they are produced in the leaf axils. The fruit is a small nut 4–5 mm long, usually with three spines, two basal and one

apical Apical means "pertaining to an apex". It may refer to: *Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features loc ...

, 1–12 mm long. Plants with the two basal nut spines very short are sometimes distinguished as ''Ceratophyllum demersum'' var. ''apiculatum'' (Cham.) Asch., and those with no basal spines sometimes distinguished as ''Ceratophyllum demersum'' var. ''inerme'' Gay ex Radcl.-Sm.Flora of China
''Ceratophyllum demersum''
/ref>Flora of North America
''Ceratophyllum demersum''
/ref>Flora of NW Europe
''Ceratophyllum demersum''
/ref>Blamey, M. & Grey-Wilson, C. (1989). ''Flora of Britain and Northern Europe''. Huxley, A., ed. (1992). ''New RHS Dictionary of Gardening''. Macmillan . It can form turions: buds that sink to the bottom of the water that stay there during the winter and form new plants in spring.

Distribution and habitat

''Ceratophyllum demersum'' grows in lakes, ponds, and quiet streams with summer water temperatures of 15-30 °C and a rich nutrient status. In North America, it occurs in the entire US and Canada, except Newfoundland. In Europe, it has been reported as far north as at a latitude of 66 degrees in Norway. Other reported occurrences include China, Siberia (at 66 degrees North),

Burkina Faso Burkina Faso (, ; , ff, 𞤄𞤵𞤪𞤳𞤭𞤲𞤢 𞤊𞤢𞤧𞤮, italic=no) is a landlocked country in West Africa with an area of , bordered by Mali to the northwest, Niger to the northeast, Benin to the southeast, Togo and Ghana to th ...

and in the Volta River in Ghana (Africa), Vietnam, and New Zealand (introduced).ISSG: distribution of C. demersum
/ref> ''Ceratophyllum demersum'' grows in still or very slow-moving water.

Invasive status

Hornwort is a declared weed under the Tasmanian Weed Management Act 1999 in Tasmania, Australia, and is classed as an unwanted organism in New Zealand.

Ecology

''C. demersum'' has

allelopathic Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have ben ...

qualities as it excretes substances that inhibit the growth of

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. ...

and

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...

(

blue-green algae Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...

). Its dense growth can outcompete native underwater vegetation, leading to

loss of biodiversity Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...

. In New Zealand, it has caused problems with hydroelectric power plants.

Cultivation and uses

This species is often used as a floating

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...

plant in both coldwater and tropical aquaria. Though without roots, it may attach itself to the substrate or objects in the aquarium. Its fluffy, filamentous, bright-green leaves provide excellent cover for newly hatched fish. It is propagated by cuttings.Hiscock, P. (2003). ''Encyclopedia of Aquarium Plants''. Interpret Publishing, United States and Canada . It is frequently used as a model organism for studies of plant physiology. One of the reasons for this is that it allows studies on shoot effects without influence of a root, which often makes interpretation of nutrition and toxicity experiments difficult in terrestrial plants. As it is free floating and therefore does not require a solid substrate, it has been used successfully in the biological life support systems "Aquarack/CEBAS" and "Omegahab" on space flights Hornwort plants or the epiphytes they support have been shown to degrade the herbicide atrazine.Rupassara, S. I., R.A. Larson, G.K. Sims, and K.A. Marley. 2002 Degradation of atrazine by hornwort in aquatic systems. Bioremediation Journal 6(3): 217-224. In aquaria this plant appears to drop all its leaves when exposed to products designed to kill snails. The stems can recover relatively quickly, growing new leaves within a few weeks.

References

External links

{{Taxonbar, from=Q157385 demersum Freshwater plants Flora of Europe Flora of Asia Flora of Africa Flora of North America Flora of South America Flora of Australia Plants described in 1753 Taxa named by Carl Linnaeus