Regnellidium
（重定向自Regnellidium diphyllum）
Regnellidium is a monotypic genus of ferns of family Marsileaceae.
The single living species, Regnellidium diphyllum, the two-leaf water fern, is native to southeastern Brazil and adjacent regions of Argentina. It resembles its relatives from the genus Marsilea, but has 2-lobed leaves (rather than 4). This fern is sometimes grown in aquaria. It is the only non-flowering plant that produces latex.