Pontederiaceae

Pontederiaceae is a family of flowering plants. The APG IV system of 2016 (unchanged from the APG III system of 2009, the APG II system of 2003 and the APG system of 1998) places the family in the order Commelinales, in the commelinid clade, in the monocots. It is a small family of heterostylous aquatic plants, occurring in tropical and subtropical waters. Charles Darwin was interested in the specialized form of heterostyly found in the family, known as tristyly. Not all of the species are heterostylous. The family contains six genera with a total of 34 known species. It is best known for the water hyacinth (Eichhornia crassipes), which is an invasive species in many waterways. The highly modified Hydrothrix gardneri is a submerged aquatic with a two-flowered pseudanthium.