川苔草科又名河苔草科或川草科，共有48属约270种，分布在全世界的热带和亚热带地区。中国有3属共3种，分布在云南和福建，是被保护物种。

本科植物为水生草本；植物体退化成扁平或枝状的叶状体，形似苔、藓、藻类或地衣，生长在河流甚至湍急的瀑布中，一年生或多年生，没有根，有时有根状物附着在水中的石头上。

1981年的克朗奎斯特分类法单独设立一个川苔草目，属于蔷薇亚纲，1998年根据基因亲缘关系分类的APG 分类法认为无法放在任何一个目中，直接放在蔷薇分支之下，并分出一个三裂科，2003年经过修订的APG II 分类法将三裂科合并到本科，一同放在金虎尾目中。

Podostemaceae (riverweed family) is a family in the order Malpighiales. It comprises about 50 genera and 250 species of more or less thalloid aquatic herbs.

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 (perhaps even just a single river or waterfall). 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.