Myriophyllum mattogrossense (Haloragaceae), a rare lowland watermilfoil new to Bolivia

Myriophyllum mattogrossense is reported as new to Bolivia. This rare Watermilfoil of the Amazon Basin was previously known only from the original area of discovery in Brazil, one locality in the lowlands of Peru, and one in Ecuador. Notes on morphology, including a terrestrial growth form, and habitat are given, and a key is provided to differentiate the South American taxa of Myriophyllum.