1 Plant minute, consisting of filaments or thalli (undifferentiated into leaves, stems, and roots), generally a single cell thick, usually with abundant single-celled gemmae (specialized budlike groups of cells for asexual reproduction), and superficially resembling bryophytes in lacking vascular tissue; [usually epipetric on vertical or overhanging bedrock; [Pteridophytes]

1 Plant more complex, with vascular tissue, with stems (or rhizomes), leaves, and roots, the leaves generally > 1 cell thick (except in sporophytes of Hymenophyllaceae), reproducing by spores; [growing in very diverse habitats, including on bedrock]; [Lycophytes, Pteridophytes].

..2 Plant aquatic, either floating and unattached, or rooting and largely submersed

..2 Plant of various habitats, including wetlands, where sometimes growing in soils saturated or intermittently flooded, but not aquatic.

....3 Leaves ‘un-fern-like’: unlobed, variously awl-shaped, scale-like, terete, strap-shaped, or palmately lobed; [Lycophytes or Pteridophytes]

....3 Leaves ‘fern-like’: variously lobed or divided, ranging from pinnatifid to 4-pinnate; [Pteridophytes].

......4 Leaf blades (not including the petiole) small, < 30 cm long or wide (some species will key either here or in the next lead).

........5 Epipetric or epiphytic, growing on rock, tree bark, walls, or over rock in thin soil mats or in small soil pockets

........5 Terrestrial, growing in soil, not associated with rock outcrops

......4 Leaf blades medium to large, > 30 cm long or wide.

..........6 Epipetric or epiphytic, growing on rock, walls, over rock in thin soil mats or in small soil pockets, or on tree trunks

..........6 Terrestrial, growing in soil, not associated with rock outcrops