Littorella is a genus of two to three species of aquatic plants. Many plants live their entire lives submersed, and reproduce by , but some are only underwater for part of the year, and flower when they are not underwater.
Some authors have treated L. uniflora and L. americana to be one species, but molecular data show L. americana to be more closely related to L. australis than it is to L. uniflora, which argues for recognizing three species. Other considerations, such as the wider range and more frequent flowering of L. uniflora, also argue for separate species. It seems likely that the genus originated in Europe and first spread to North America, and from there to South America, with both events happening in the Pleistocene or later.
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