They are found mostly intropical andsubtropical areas worldwide.[3] Many species are found in a very small geographic area, often even just a single river or waterfall.[4][5] Because of their small range, many species are seriously threatened, especially fromhabitat loss (for example, due todams flooding their habitat).[5][6]
Riverweeds adhere to hard surfaces (generally rock) in rapids and waterfalls ofrivers. 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.[7]
In many rivers, Podostemaceae are an important food source for a wide range of animals. For example, the tadpoles of the Africangoliath frog (world's largest frog) feed only onDicraeia warmingii,[8] and in South America severalserrasalmid fish (Mylesinus,Ossubtus,Tometes andUtiaritichthys) mainly feed on Podostemaceae.[9]
The Podostemaceae are related to the familiesClusiaceae,Hypericaceae (the St. John's wort family, which is sometimes treated as a subfamily of Clusiaceae), andBonnetiaceae.[11][12] In the classification system ofDahlgren Podostemaceae were placed as a single family in the Podostemales order, which was the only order in thesuperorder Podostemiflorae (also called Podostemanae).
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.[13]
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 theCornales.
^Satoshi Koi; Rieko Fujinami; Namiko Kubo; Ikue Tsukamoto; Rie Inagawa; Ryoko Imaichi; Masahiro Kato (2006). "Comparative anatomy of root meristem and root cap in some species of Podostemaceae and the evolution of root dorsiventrality".American Journal of Botany.93 (5):682–692.doi:10.3732/ajb.93.5.682.PMID21642132.
^van der Sleen, P.; J.S. Albert, eds. (2017).Field Guide to the Fishes of the Amazon, Orinoco, and Guianas. Princeton University Press. pp. 173–196.ISBN978-0691170749.
^Gustafsson, Mats H. G. (2002). "Phylogeny of Clusiaceae Based onrbcL sequences".International Journal of Plant Sciences.163 (6):1045–1054.doi:10.1086/342521.JSTOR3080291.S2CID85307271.
^Katayama, N., Koi, S., Sassa, A. et al. Elevated mutation rates underlie the evolution of the aquatic plant family Podostemaceae.Communications Biology 5, 75 (2022).https://doi.org/10.1038/s42003-022-03003-w
