Littorella
Littorella is a genus of two to three species of aquatic plants. Many plants live their entire lives submersed, and reproduce by stolons, but some are only underwater for part of the year, and flower when they are not underwater. Classification. Molecular data show "Littorella" to be sister to the rest of the genus "Plantago". Thus, cladistics would allow it to be considered either as a separate genus or as part of "Plantago". Some researchers, particularly Rahn in the 1990s, have considered "Littorella" to be located within "Plantago", but this does not seem to be required given the molecular  data and a closer look at morphology. Species. 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. Distribution. The European species  is found in a wide range of habitats, from arctic to Mediterranean. The North and South American species are found in a more limited range of temperate climates.