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Key to Adiantum

Pteridaceae

Adiantum

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1 Petioles and rachises pubescent; [of the Coastal Plain of FL, GA, AL, and LA].
  2 Leaves broader than long, dichotomously divided at the summit of the petiole, the two main branches pedately branched, fanlike; ultimate leaf segments hairy with multicellular hairs on the lower surface; rachises hispid; false indusia roundish; [formosum clade]
  2 Leaves longer than broad, pinnately divided, with a main central axis, not fanlike; Ultimate leaf segments glabrous on the lower surface; rachises strigose; false indusia crescent-shaped.
    3 Leaf segments glaucous below; [peruvianum clade]
    3 Leaf segments green below; [tetraphyllum clade]
1 Petioles and rachises glabrous; [collectively widespread].
      4 Leaves broader than long, dichotomously divided at the summit of the petiole, the two main branches pedately branched, fanlike; ultimate segments oblong, > 2× as long as broad; [pedatum clade]
      4 Leaves longer than broad, pinnately divided, with a main central axis, not fanlike; ultimate segments rhombic, about as long as broad (usually 0.7-1.3× as long as broad).
        5 Leaflets 2-8 cm long, 1-7 cm wide; [of s. FL]; [peruvianum clade].
          6 Leaflets 5-8 cm long, 2.5-7 cm wide
          6 Leaflets 2-5 cm long, 1-3 cm wide
        5 Leaflets 0.5-3 cm long, 0.5-3 cm wide; [collectively more widespread].
             7 Blackish-brown color of the stalks extending into the base of the ultimate segments, making 1 or 2 dichotomous branchings before fading to green; [of VA, KT, and MO southwards]; [capillus-veneris clade]
             7 Blackish-brown color of the stalks ending abruptly at the base of the ultimate segments in a cupule-like swelling (use at least 10× magnification); [of n. FL southwards]; [tenerum clade]