Vallisneria spiralis Erasmus Darwin 1789

Hydrophily is a fairly uncommon form of

pollination Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds ...

whereby

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...

is distributed by the flow of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

s, particularly in

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s and

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...

s. Hydrophilous species fall into two categories: (i) Those that distribute their pollen to the surface of water. e.g. ''Vallisnerias male flower or pollen grain are released on the surface of water, which are passively carried away by water currents; some of them eventually reach the female flower (ii) Those that distribute it beneath the surface. e.g. seagrasses in which female flower remain submergered in water and pollen grains are released inside the water.

Surface pollination

Surface pollination is more frequent, and appears to be a transitional phase between

wind pollination Anemophily or wind pollination is a form of pollination whereby pollen is distributed by wind. Almost all gymnosperms are anemophilous, as are many plants in the order Poales, including grasses, sedges, and rushes. Other common anemophilous plan ...

and true hydrophily. In these the pollen floats on the surface and reaches the stigmas of the female flowers as in ''

Hydrilla ''Hydrilla'' (waterthyme) is a genus of 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 ...

'', ''

Callitriche ''Callitriche'' is a genus of largely aquatic plants known as water-starwort. Previously, it was the only genus in the family Callitrichaceae. However, according to the APG II system this family is now included in the Plantaginaceae (plantain fam ...

'', ''

Ruppia ''Ruppia'', also known as the widgeonweeds, ditch grasses or widgeon grass, is the only extant genus in the family Ruppiaceae, with eight known species. These are aquatic plants widespread over much of the world. The genus name honours Heinrich ...

'', ''

Zostera ''Zostera'' is a small genus of widely distributed seagrasses, commonly called marine eelgrass, or simply seagrass or eelgrass, and also known as seaweed by some fishermen and recreational boaters including yachtsmen. The genus ''Zostera'' con ...

'', ''

Elodea ''Elodea'' is a genus of 6 species of aquatic plants often called the waterweeds described as a genus in 1803. Classified in the frog’s-bit family (Hydrocharitaceae), ''Elodea'' is native to the Americas and is also widely used as aquarium vege ...

''. In ''

Vallisneria ''Vallisneria'' (named in honor of Antonio Vallisneri) is a genus of freshwater aquatic plant, commonly called eelgrass, tape grass or vallis. The genus is widely distributed in tropical and subtropical regions of Asia, Africa, Europe, and North ...

'' the male flowers become detached and float on the surface of the water; the anthers are thus brought in contact with the stigmas of the female flowers. Surface hydrophily has been observed in several species of ''

Potamogeton ''Potamogeton'' is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed (''Elodea canadensis'' ...

'' as well as some marine species.

Submerged pollination

Species exhibiting true submerged hydrophily include ''

Najas ''Najas'', the water-nymphs or naiads, is a genus of aquatic plants. It is cosmopolitan in distribution, first described for modern science by Linnaeus in 1753. Until 1997, it was rarely placed in the Hydrocharitaceae,Angiosperm Phylogeny Grou ...

'', where the pollen grains are heavier than water, and sinking down are caught by the stigmas of the extremely simple female flowers, ''

Posidonia australis ''Posidonia australis'', also known as fibre-ball weed or ribbon weed, is a species of seagrass that occurs in the southern waters of Australia. It forms large meadows important to environmental conservation. Balls of decomposing detritus from ...

'' or ''

Zostera marina ''Zostera marina'' is a flowering vascular plant species as one of many kinds of seagrass, with this species known primarily by the English name of eelgrass with seawrack much less used, and refers to the plant after breaking loose from the submer ...

'' and ''Hydrilla''.

Evolution

Hydrophily is unique to obligate submersed aquatic angiosperms with sexually reproductive parts completely submerged below the water surface. Hydrophily is the adaptive evolution of completely submersed angiosperms to aquatic habitats. True hydrophily occurs in 18 submersed angiosperm genera, which is associated with an unusually high incidence of unisexual flowers. CC-BY icon

Text was copied from this source, which is available under
Creative Commons Attribution 4.0 International License

References

Sources

* * {{pollination Plant morphology Pollination it:Impollinazione#Impollinazione idrogama