Ophioglossum, or Adder's-Tongue, a genus of Pteridophyta (q.v.) forming, with the moonworts (q.v.) (Botrychium), the class Ophioglossacea-, which, though commonly classed with ferns (q.v.), differ from them in several important structural characters. The genus includes a small number of species, one of which is British, scattered over most of the globe, none over a foot in height. The prothallium is subterranean, destitute of chlorophyll, tuber-like, and monoecious. The antheridia and archegonia are both deeply sunk in its surface. The stem of the sporophore stage is very short, unbranched, very slow in growth, containing no sclerenchyma and having a three-sided apical cell. A very few leaves are produced singly from the stem and from below each an unbranched root also with a three-sided apical cell. These roots sometimes bear adventitious buds. The leaves are not circinate in vernation. Each of them branches fnto a barren and a fertile lobe. The former is a leathery, ovate, sheathing, net-veined leaflet; and the latter a spike-like "fructification," along which the sporangia originate endogenously in two rows, each from a group of cells (eu-sporangiate).