Water Ferns (Aquatic Ferns)

This group gathers Ferns and Fern Allies subcategory members belonging to the water ferns, a small number of unrelated fern lineages that have independently adapted to a fully or partially aquatic lifestyle, floating freely on the surface of still or slow-moving fresh water rather than rooting in soil. It spans the mosquito ferns of the genus Azolla, tiny floating ferns that host a symbiotic, nitrogen-fixing cyanobacterium and have been used for centuries as a natural fertilizer in rice paddies across parts of Asia, the floating ferns of the genus Salvinia, several species of which have become aggressive, waterway-choking invasive weeds far outside their native range, and the water clovers of the genus Marsilea, unusual among ferns for a four-lobed leaf shape that closely resembles a four-leaf clover despite no close relation to true clover at all. Every member gathered here reproduces via specialized, water-dispersed spore structures rather than the exposed sori typical of most land-dwelling ferns.