Salviniales

Salviniales is an order of aquatic ferns whose living members include the floating genera Salvinia and Azolla and the submerged genus Marsilea.

Fern: A vascular plant that reproduces by spores rather than seeds and typically has fronds. Salviniales belongs to the fern lineage despite its specialized aquatic habit.
Sporocarp: A compact, protective structure containing spore-producing organs in certain ferns. Salviniales often enclose their sporangia in sporocarps that resist drying and other stresses.
Azolla: A genus of tiny floating aquatic ferns that hosts nitrogen-fixing cyanobacteria. Azolla is the order's best-known agricultural fern and a distinctive nitrogen-fixing symbiosis.
Salvinia: A genus of floating aquatic ferns with leaves arranged in whorls and submerged, root-like leaves. It is one of the two best-known living genera within Salviniales.
Sporophyte: The diploid, spore-producing generation in the life cycle of plants and many algae. The conspicuous aquatic plants of Salviniales are sporophytes.
Sporangium: A structure in which spores are produced, usually by meiosis. The order's heterosporous reproduction depends on distinct microsporangia and megasporangia.
Azolla as biofertilizer: The use of Azolla biomass to add nitrogen and organic matter to agricultural soils, especially rice paddies. Farmers cultivate Azolla in flooded fields and incorporate its biomass as fertilizer.
Marsilea: A genus of aquatic or semi-aquatic ferns whose four-part leaves resemble four-leaf clovers. Unlike floating Salvinia and Azolla, many Marsilea species root in mud and bear emergent leaves.
Heterospory: The production of two distinct spore types: smaller microspores and larger megaspores. Living water ferns produce separate male and female spores, unlike most ferns.
Anabaena azollae: A nitrogen-fixing cyanobacterium that lives in cavities of Azolla leaves. This symbiont supplies biologically available nitrogen to Azolla.

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Leptosporangiate fernBroader topic: Its aquatic members demonstrate the group's adaptation to life on water.