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.
Those of Ophioglossum are cylindrical, while the dorsiventral prothallus of Botrychium bears the sexual organs on the upper surface.
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 fertile branch or branches are situated on the adaxial surface of the leaves, and may be simple, as in Ophioglossum (fig.