Regnellidium is a monotypic genus of ferns of family Marsileaceae.

Regnellidium diphyllum.jpg
Scientific classification e
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Order: Salviniales
Family: Marsileaceae
Genus: Regnellidium

Regnellidium diphyllum Lindm.
Regnellidium upatoiensis

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.

A fossil assigned to the species Regnellidium upatoiensis has been found in Cretaceous deposits of the eastern United States.


  • Lupia, R.; Schneider, H.; Moeser, G. M.; Pryer, K. M.; Crane, P. R. (2000). "Marsileaceae Sporocarps and Spores from the Late Cretaceous of Georgia, U.S.A". International Journal of Plant Sciences. 161 (6): 975–988. doi:10.1086/317567. S2CID 16981770.
  • Mabberley, D. J. (1997). The Plant-Book. Cambridge University Press.