In the three genera, Ophioglossum, Botrychium and Helminthostachys, there is an underground rhizome, from which one leaf or a few leaves with sheathing bases are produced annually; the roots arise in more or less definite relation to the insertion of the leaves.
The latter are simple, or irregularly lobed in Ophioglossum, more or less compoundly pinnate in Botrychium and palmately pinnate in Helminthostachys.
The endodermis and pericycle surround the whole stele in Botrychium and Helminthostachys; in Ophioglossum each bundle has a separate sheath.
In the roots of Ophioglossum and Botrychium and in the first formed roots of Helminthostachys an endophytic fungus is present, forming a mycorhiza - the stele in the larger roots has the usual radial arrangement of xylem and phloem; monarch roots occur in Ophioglossum.
The spike is most simple in Ophioglossum, where it bears on each side a row of large sporangia, which hardly project from the surface, the vascular bundles occupying a central position.
The spike of Helminthostachys corresponds to that of Ophioglossum, but in it the sporangia are borne on two lateral rows of branched sporangiophores.
Those of Ophioglossum are cylindrical, while the dorsiventral prothallus of Botrychium bears the sexual organs on the upper surface.
Of the Ophioglossaceae there are no satisfactory examples; one of the few fossils compared with a recent species, Ophioglossum palmatum, was described several years ago from Triassic rocks under the name Cheiropteris, but the resemblance is one of external form only, and practically valueless as a taxonomic criterion.