''Ceratopteris'' is the only

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

among

homosporous In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae ...

ferns that is exclusively aquatic. It is pan-tropical and classified in the Parkerioideae subfamily of the family

Pteridaceae Pteridaceae is a family of ferns in the order Polypodiales, including some 1150 known species in ca 45 genera (depending on taxonomic opinions), divided over five subfamilies. The family includes four groups of genera that are sometimes recogni ...

Description

Erect aquatic or subaquatic ferns of moderate size. Rhizome short, fleshy, horizontal and ascending to erect, loosely rooted in the mud or +/- floating, radial, dictyostelic with numerous meristeles and medullary strands, young parts bearing thin, ovate, +/- cordate, clathrate scales. Fronds stipitate, the stipes fleshy, with numerous longitudinal air canals, abaxially rounded and ribbed, adaxially flattened, vascular bundles in a peripheral ring, one with each rib and several to the adaxial side, and several smaller medullary strands; lamina dimorphic, sterile fronds +/- spreading, 2–3-pinnatifid with broad membranous lobes, venation reticulate without included free veinlets, often with proliferous buds in the axils; fertile fronds erect, longer, narrower and more divided than the sterile, the lobes strongly recurved to completely cover the adiaxial surface, venation longitudinal, branching at the bases of the lobes. Sporangia solititary, scattered along the veins, exindusiate but protected by the continuous reflexed margin of the lamina, large, short-stalked, annulus broad, irregular, of 30–70 thickened cells, or lacking, containing 16 to 32 spores. Spores large, trilete, ribbed with irregular long meshes.

Taxonomy

''Ceratopteris'' was long placed in the monogeneric family Parkeriaceae, thought to be unique because of its aquatic adaptations. However, recent genetic analysis has shown it to be clearly allied with ''

Acrostichum ''Acrostichum'' is a fern genus in the Parkerioideae subfamily of the Pteridaceae. It was one of the original pteridophyte genera delineated by Linnaeus. It was originally drawn very broadly, including all ferns that had sori apparently "acr ...

'' in the subfamily Parkerioideae, within the family

Species

At one time, some authorities recognized only one species; now some authorities recognize only four species. However, recent work by Masuyama and Watano '' has suggested that C. thalictroides'' actually consists of four cryptic species (''thalictroides'', ''froesii'', ''gaudichaudii'', ''oblongibloba''). *'' Ceratopteris cornuta'' (P. Beauv.) Le Prieur; Ann. Sci. Nat. 19: 103. t. 4A (1830) *'' Ceratopteris froesii'' Brade, Arch. Jard. Bot. Rio de Janeiro 18: 31 (1964). *'' Ceratopteris gaudichaudii'' Brongn.; Bull. Soc. Philom. 187 (1821) *'' Ceratopteris oblongiloba'' Masuyama & Watano—Acta Phytotax. Geobot. 61(2): 84 (-85; figs. 3-4). 2010 ov 2010 *'' Ceratopteris pteridoides'' (Hook.) Hieron.; Bot. Jahrb. Syst. 34: 561 (1905) *'' Ceratopteris richardii'' Brongn.; Dict. Class. Hist. Nat. 3: 351 (1823) - "C-fern" *'' Ceratopteris thalictroides'' (L.) Brongn.; Bull. Sci. Soc. Philom. Paris, sér. 3, 8: 186 (1821)

Distribution and habitat

This widespread genus of four to six species inhabits the humid

tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred ...

. ''Ceratopteris'' is also important in the study of

pteridophytes A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as " cryptogams", meaning that their means of reproduction is hidden. ...

and is a commonly used model organism for use in

genomic Genomics is an interdisciplinary field of biology focusing on the structure, function, evolution, mapping, and editing of genomes. A genome is an organism's complete set of DNA, including all of its genes as well as its hierarchical, three-dim ...

studies, due to the ease and rapidity with which it can be grown in

laboratories A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physici ...

, as well as having well-characterized phenotypes. Patented strains of this plant have been developed.

Outcrossing and self-fertilization

gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...

is one of the two alternating multicellular phases of the fern life cycle. The gametophyte is haploid. The other stage is the diploid sporophyte. A gametophyte is a multicellular organism that develops from a haploid spore (that has one set of chromosomes). ''Ceratopteris thalictroides'' has two types of gametophytes with different sexual expression: these types are

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have ...

and male. Hermaphroditic gametophytes have one or several

archegonia An archegonium (pl: archegonia), from the ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female ga ...

and a few

antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also t ...

. Archegonia are multicellular structures of the gametophyte that produce and contain the ovum or female

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

. The corresponding male organ is the antheridium, a haploid organ producing and containing sperm. The second of the two types of gametophyte are male that produce only antheridia. When ''Ceratopteris richardii'' ferns are grown alone they develop into hermaphrodites (with mainly female archegonia). However, plants that grow near established genetically identical individuals develop into males. The hermaphrodite secretes a

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

( antheridiogen) that tells others nearby to be male. Thus when plants are near each other

outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a useful ...

is promoted. Self-fertilization predominates when there is no nearby partner.

Toxicity

The plants may have

carcinogenic A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...

properties.

Uses

''Ceratopteris'' is a fairly popular aquarium plant, often sold under the name "water sprite." It may be grown as an emersed but natant (floating) plant, or as an immersed plant rooted in the substrate. Under the right conditions the plants will grow fully emerse erect leaves. Under a bright light the plants can grow fast, and be used to help cycle an aquarium. This plant is often used as a vegetable, particularly in Asia.