Littorella lacustris

Littorella uniflora (vernacular name: (American) shoreweed) is a species of aquatic flowering plant native to the Azores, Morocco, most of Europe excluding the dry southeast, Iceland, and the Faroes. It prefers to live mostly submerged in nutrient-poor freshwater habitats. When submerged, it draws CO2 mostly through its roots and uses a mix of crassulacean acid metabolism (CAM) and C3 carbon fixation for photosynthesis. If the water level drops and exposes the roots, it ceases using CAM.