The Ophioglossaceae are homosporous, and the prothalli, which are known in species of all three genera, are subterranean and saprophytic (fig.
Usually it grows exposed to the light and contains chlorophyll, but subterranean saprophytic prothalli also occur in the Lycopodiaceae and Ophioglossaceae (fig.
The important bearing of this question on the relationship of the Ophioglossaceae to the phyla of the Filicales and Lycopodiales will be obvious.
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.
In these respects, in the megaphyllous habit and in certain anatomical features, the Ophioglossaceae approach the Filicales.