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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 (often hirsute, but sometimes glabrescent at maturity in A. caudatum); false indusia crescent-shaped.
    3 Tips of fronds (the rachis) often with a prolonged, whip-like stolon rooting at the tip and forming new plantlet
    3 Rachis apices lacking a terminal, rooting, tip (plantlets never present at rachis or frond tips).
      4 Leaf segments glaucous below; [peruvianum clade]
      4 Leaf segments green below; [tetraphyllum clade]
1 Petioles and rachises glabrous; [collectively widespread].
        5 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]
        5 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).
          6 Leaflets 2-8 cm long, 1-7 cm wide; [of s. FL]; [peruvianum clade].
          6 Leaflets 0.5-3 cm long, 0.5-3 cm wide; [collectively more widespread].
               8 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]
               8 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]