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Key A1: pteridophytes reduced to thalloid or filamentous, free-living gametophytes

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1 Gametophytes filamentous in part or in whole, forming felt-like mats.
  2 Gametophytes strictly filamentous; [inland physiographic provinces, on ceilings and back walls of rock grottos]
  2 Gametophytes filamentous and also bearing flattened blades tipped by gemmae; [rotting wood in the Coastal Plain]
1 Gametophytes thalloid, ribbon-like and branched.
    3 Gemmae absent or spatulate (the gemma > 1 cell wide)
    3 Gemmae with cells uniseriate (the gemma 1 cell wide)