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Podostemaceae A family of aquatic herbs whose structure is often modified into a thallus with anchoring roots. The flowers are tiny, bisexual, regular, and reduced. The fruit is a capsule. They are locally common and conspicuous, especially in tropical America, and rare and disjunct in the eastern tropics. They may be related to the Saxifragaceae. There are 50 genera, comprising 275 species, occurring mainly in the tropics where they are confined to swiftly flowing rivers.