Podostemaceae (riverweed family), a family in the order Malpighiales, comprise about 46 genera and ca 300 species of more or less thalloid aquatic herbs.
Flowering riverweed in the Dordogne river
Riverweeds adhere to hard surfaces (generally rock) in rapids and waterfalls of rivers. They are found mostly in tropical 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 (for example, due to dams flooding their habitat). Riverweeds 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.
The Caño Cristales
river in Colombia is famous for the bright red Macarenia clavigera, a species only found in Serranía de la Macarena
The Podostemaceae are related to the families Clusiaceae, Hypericaceae (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).
In many rivers, Podostemaceae are an important food source for a wide range of animals. For example, the tadpoles of the African goliath frog (world's largest frog) feed only on Dicraeia warmingii, and in South America several serrasalmid fish (Mylesinus, Ossubtus, Tometes and Utiaritichthys) mainly feed on Podostemaceae.