Podostemaceae (riverweed family), a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

in the order

Malpighiales The Malpighiales comprise one of the largest orders of flowering plants, containing about 36 families and more than species, about 7.8% of the eudicots. The order is very diverse, containing plants as different as the willow, violet, poinsett ...

, comprise about 50 genera and

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of more or less

thalloid Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms were ...

aquatic herbs.

Distribution and habitat

They are found mostly in

tropical 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 to ...

and subtropical areas worldwide. Many species are found in a very small geographic area, often even just a single river or waterfall. Because of their small range, many species are seriously threatened, especially from

habitat loss Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

(for example, due to

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...

s flooding their habitat). Riverweeds adhere to hard surfaces (generally rock) in rapids and waterfalls of

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 w ...

s. They are submerged when water levels are high, but during the dry season they live a terrestrial existence, flowering at this time. Their root anatomy is specialized for the purpose of clinging to rocks, and in fact details of the root structure are one of the ways of classifying riverweeds.

Ecology

In many rivers, Podostemaceae are an important food source for a wide range of animals. For example, the tadpoles of the African

goliath frog The goliath frog (''Conraua goliath''), otherwise known commonly as the giant slippery frog and the goliath bullfrog, is a species of frog in the family Conrauidae. The goliath frog is the largest living frog. Specimens can grow up to in lengt ...

(world's largest frog) feed only on ''Dicraeia warmingii'', and in South America several

serrasalmid The Serrasalmidae (serrasalmids) are a family of characiform fishes, recently elevated to family status. It includes more than 90 species. The name means "serrated salmon family", which refers to the serrated keel running along the belly of these ...

fish (''

Mylesinus ''Mylesinus'' is a genus of serrasalmids from South America, where found in the eastern Amazon, Essequibo and Orinoco basins. They are rheophilic, typically found at rapids and mainly feed on Podostemaceae plants. Because of their habitat prefe ...

'', ''

Ossubtus ''Ossubtus'' is a genus of fish in the family Serrasalmidae. It contains a single species, ''Ossubtus xinguense'', the parrot pacu or eaglebeak pacu, The species is endemic to rapids in the Xingu River basin in the Brazilian Amazon.Andrade, M.C., ...

'', ''

Tometes ''Tometes'' is a genus of fish in the family Serrasalmidae found in fast-flowing rivers in northern South America. Adults of all seven species in this genus are phytophagous, feeding primarily on aquatic plants in the family Podostemaceae. The ...

'' and ''

Utiaritichthys ''Utiaritichthys'' is a genus of serrasalmid fish found in the Amazon and Orinoco basins in tropical South America. The adults are typically found in rapidly flowing water where they feed on aquatic plants in the family Podostemaceae and filame ...

'') mainly feed on Podostemaceae.

Taxonomy

The Podostemaceae are related to the families

Clusiaceae The Clusiaceae or Guttiferae Juss. (1789) (''nom. alt. et cons.'' = alternative and valid name) are a family (biology), family of plants including 13 genera and ca 750 species. Several former members of Clusiacae are now placed in Calophyllaceae ...

Hypericaceae Hypericaceae is a plant family in the order Malpighiales, comprising six to nine genera and up to 700 species, and commonly known as the St. John's wort family. Members are found throughout the world apart from extremely cold or dry habitats. '' ...

(the St. John's wort family, which is sometimes treated as a subfamily of Clusiaceae), and Bonnetiaceae. In the classification system of Dahlgren Podostemaceae were placed as a single family in the Podostemales order, which was the only order in the superorder Podostemiflorae (also called Podostemanae).

Genera

Moved to other families

*'' Hydrostachys'' from Madagascar. This genus seems to have relatively little in common with any other, and no affinity to the Podostemaceae except being aquatic; moved to its own family in the

Cornales The Cornales are an order of flowering plants, early diverging among the asterids, containing about 600 species. Plants within the Cornales usually have four-parted flowers, drupaceous fruits, and inferior to half-inferior gynoecia topped with ...

Distribution and habitat

Ecology

Taxonomy

Genera

Moved to other families

See also

References

Further reading