Podostemaceae
Podostemaceae, a family in the order Malpighiales, comprise about 50 genera and species of more or less thalloid aquatic herbs.
Distribution and habitat
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.Riverweeds adhere to hard surfaces in rapids and waterfalls of rivers. 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 feed only on Dicraeia warmingii, and in South America several serrasalmid fish mainly feed on Podostemaceae.Taxonomy
The Podostemaceae are related to the families Clusiaceae, Hypericaceae, 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.The family is divided into three subfamilies, Podostemoideae, Trisichoideae, and Weddellinoideae. Trisichoideae is the most basally diverged, and is sister to the other two subfamilies.