They are found mostly in
tropical and
subtropical 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 from
habitat loss (for example, due to
dams flooding their habitat).[5][6]
Riverweeds adhere to hard surfaces (generally rock) 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.[7]
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 (world's largest frog) feed only on Dicraeia warmingii,[8] and in South America several
serrasalmid fish (Mylesinus, Ossubtus, Tometes and Utiaritichthys) mainly feed on Podostemaceae.[9]
Taxonomy
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.[11][12] 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).
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.
^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 on rbcL sequences". International Journal of Plant Sciences. 163 (6): 1045–1054.
doi:
10.1086/342521.
JSTOR3080291.
S2CID85307271.