''Ceratophyllum'' is a cosmopolitan

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

s commonly found in ponds, marshes, and quiet streams in tropical and in temperate regions. It is the only

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

genus in the family Ceratophyllaceae,Kew World Checklist of Selected Plant Families
/ref> itself the only extant family in the order Ceratophyllales. They are usually called coontails or hornworts, although hornwort is also used for unrelated plants of the division Anthocerotophyta.

Description

''Ceratophyllum'' grows completely submerged, usually, though not always, floating on the surface of the water. The plant stems can reach 1–3 m in length. At intervals along nodes of the stem they produce rings of bright green

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

, which are narrow and often much-branched. The forked leaves are brittle and stiff to the touch in some species, softer in others. Roots are completely absent and are missing even in the embryonic stage, but sometimes they develop modified leaves with a rootlike appearance, which anchor the plant to the bottom.

Stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

ta are not present on any species. The

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

s are small and inconspicuous, with the male and female flowers on the same plant. In ponds it forms thick buds ( turions) in the autumn, which sink to the bottom and give the impression that the plant has been killed by the frost; but come spring, these will grow back into the long stems, slowly filling up the pond.Flora of China
''Ceratophyllum''
/ref>Flora of North America
''Ceratophyllum''
/ref>Blamey, M. & Grey-Wilson, C. (1989). ''Flora of Britain and Northern Europe''. Huxley, A., ed. (1992). ''New RHS Dictionary of Gardening''. Macmillan .

Taxonomy

''Ceratophyllum'' was first described by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

in 1753 with ''Ceratophyllum demersum'' as the type species. ''Ceratophyllum'' is considered distinctive enough to warrant its own family, Ceratophyllaceae, but was considered a relative of

Nymphaeaceae Nymphaeaceae () is a family of flowering plants, commonly called water lilies. They live as rhizomatous aquatic herbs in temperate climate, temperate and tropical climates around the world. The family contains five genera with about 70 know ...

and included in Nymphaeales in the

Cronquist system The Cronquist system is a list of systems of plant taxonomy, taxonomic classification system of angiosperms, flowering plants. It was developed by Arthur Cronquist in a series of monographs and texts, including ''The Evolution and Classification of ...

. Recent research has shown that it is not closely related to Nymphaeaceae or any other extant plant family. Some early molecular phylogenies suggested it was the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to all other angiosperms, but more recent research suggests that it is the sister group to the

eudicots The eudicots or eudicotyledons are flowering plants that have two seed leaves (cotyledons) upon germination. The term derives from ''dicotyledon'' (etymologically, ''eu'' = true; ''di'' = two; ''cotyledon'' = seed leaf). Historically, authors h ...

. This notion was supported upon sequencing of the '' C. demersum'' genome in 2020. The APG IV system placed the family in its own order, the Ceratophyllales, and gives the following cladogram.Angiosperm Phylogeny Web
Ceratophyllales
/ref>

Species

The subgeneric division of the genus ''Ceratophyllum'' into its appropriately recognized species, subspecies, and varieties is not settled. More than 30 species have been described and published. A narrow interpretation of this work rejects over 23 of these taxa as variants, accepting only 7 species. This narrow interpretation lumps to the point of failing to give these potential species the taxonomic importance of even being named on a subspecific or varietal level. The genus as narrowly defined in this manner contains the following seven species:Germplasm Resources Information Network
''Ceratophyllum''
/ref>Flora Europaea
''Ceratophyllum''
/ref> * '' Ceratophyllum australe'' Griseb. * '' Ceratophyllum demersum'' L. (rigid/common hornwort) – cosmopolitan * ''

Ceratophyllum echinatum ''Ceratophyllum echinatum'', known as prickly hornwort, spiny hornwort, or spiny coontail, is an aquatic, perennial plant found in North America. Its name comes from fruits, which have a warty surface and long spines. Spiny hornwort can be found ...

'' A.Gray (spiny hornwort) – North America * '' Ceratophyllum muricatum'' Cham. (prickly hornwort) – Near-cosmopolitan * '' Ceratophyllum platyacanthum'' Cham. – Europe and Asia * '' Ceratophyllum submersum'' L. (soft/tropical hornwort) – Europe, Middle-East, Central Asia, northern and central Africa, Florida, and Dominican Republic * '' Ceratophyllum tanaiticum'' Sapjegin

Phylogeny

A 2018 phylogenetic analysis of the above species gives the below cladogram. It finds support for 4 species being monophyletic, while 3 others are paraphyletic. It found ''C. australe'' to be a divergent lineage of ''C. tanaiticum'', rendering ''C. tanaiticum'' paraphyletic. Nonetheless, it still regards ''C. australe'' as a separate species due to significant morphological differences and its geographic isolation from the rest of ''C. tanaiticum''. '' C. demersum'' and ''C. platyacanthum'' were recovered as paraphyletic with respect to each other, and as such they could possibly be considered one species, although their morphologies and ecologies are distinct.

References

External links

Ceratophyllaceae of Mongolia in FloraGREIF
{{Authority control Angiosperm genera Freshwater plants