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a genus of ferns of the family Ophioglossaceae, including mostly low herbs. Only a few tropical species are epiphytic, with the leaves reaching 2.7 m in length. The leaves are for the most part entire or lobed. The sporangia are sessile and open transversely. Some species reproduce vegetatively by means of adventitious buds formed on the roots. The prothallia (gametophytes) are usually cylindrical and subterranean; those developing aboveground contain chlorophyll. There are about 45 species, distributed in the tropical and, less commonly, temperate zones of both hemispheres. Of the three or four species found in the USSR, the most common is the adder’s-tongue (O. vulgatwn), which grows in moist meadows and amid shrubbery.