The sporangia of the Psilotaceae are associated in synangia, which occupy the same position relatively to the sporophyll, as the single sporangium of Lycopodium or the group of sporangia in Spenophyllum majus.
Typically Marattiaceous sori, consisting of exannulate sporangia united to form synangia, are frequent, and are almost always found on fronds with the character of Pecopteris, large, repeatedly pinnate leaves, resembling those of Cyatheaceae or some species of Nephrodium.
In all these genera there is an obvious similarity to the synangia of Kaulfussia, while in some respects Marattia or Danaea is approached.
In the genus Danaeites, from the Coal Measures of the Saar, the synangia are much like those of the recent Danaea, each sporangium opening by an apical pore.
The genus Corynepteris of Baily is interesting from the fact that its sporangia, while individually similar to those of Zygopteris, were grouped in sori or synangia, resembling those of an Asterotheca.