Superficially similar to Lycopodium , but often prostrate, creeping with angular strobili. Distinctive by being heterosporous and endosporic . Diverse and the subject of much taxonomic confusion - lumping vs. splitting. About 12,000 species worldwide. Hatch, et al.
Spore germination occurs after rupture of the sporocarp wall.
Subsequent hydration produces a gelatinous structure that carries the sori and spores into the water. 3 genera, ca. Very distinctive ferns.