Regnellidium is a monotypic genus of fern

Fern

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

s of family Marsileaceae

Marsileaceae

The Marsileaceae are a small family of heterosporous aquatic and semi-aquatic ferns, though at first sight they do not physically resemble other ferns. The group is commonly known as the "pepperwort family" or as the "water-clover family" because the leaves of the genus Marsilea superficially...

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The single living species, Regnellidium diphyllum, Two-leaf Water Fern, is native to South Eastern Brazil and adjacent regions of Argentina. It resembles its relatives from the genus Marsilea

Marsilea

Marsilea is a genus of approximately 65 species of aquatic ferns of the family Marsileaceae.These small plants are of unusual appearance and do not resemble common ferns...

, 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

Latex

Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...

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A fossil assigned to the species Regnellidium upatoiensis has been found in Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 deposits of the eastern United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

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