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Key to Argyrochosma

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1 Lower surface of leaf blades densely covered with white farina; ultimate leaf segments not articulate (the brown color of the petiole continuing into the midvein of the segment, most visible on the upper side of the segment)
1 Lower surface of leaf blades glabrous; ultimate leaf segments articulate (the brown color of the petiole ending abruptly at the segment base)

Key to Pteridaceae

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1 Gametophytes only present; [subfamily Vittarioideae]
1 Sporophytes present.
  2 Leaves undissected and unlobed, linear, 10-60 cm long and 1-3 mm wide; [subfamily Vittarioideae]
  2 Leaves dissected, not linear, > 20 mm wide.
    3 Sori round or oblong, distinct and separate along the pinnule margins; leaves bright-green, glabrous, herbaceous, delicate, and flexible (darker green, thicker, and hairy in A. hispidulum); [subfamily Vittarioideae]
    3 Sori continuous along the pinnule margins (or across the blade in Acrostichum); leaves mostly dark-green or glaucous, often pubescent, coriaceous, tough, and stiff (except Ceratopteris).
      4 Plant aquatic or subaquatic, pale green, delicate; [subfamily Ceratopteridoideae]
      4 Plant epipetric or terrestrial (except Acrostichum), usually dark or bluish green and coriaceous.
        5 Fertile pinnae with entire lower surface covered by sporangia; leaves 1.5-5 m long; [of wetlands, n. FL southward]; [subfamily Ceratopteridoideae]
        5 Fertile pinnae with sori marginal; leaves < 0.5 m long; [of rocky sites, collectively widespread].
          6 Leaves strongly dimorphic, the fertile leaves obviously longer than the sterile and with narrow elongate ultimate segments; [subfamily Cryptogrammoideae]
          6 Leaves essentially monomorphic.
             7 Petioles with alternating longitudinal grooves (2 or 3) and ridges on the upper surface; [subfamily Pteridoideae].
               8 Lower surface of leaf blades with white or yellow farina; sporangia along the veins, not covered by the reflexed leaf margin; [of peninsular FL in our region]
               8 Lower surface of leaf blades lacking farina; sporangia submarginal, typically covered by the reflexed leaf margin; [widespread in our region]
             7 Petioles rounded, flattened, or with a single groove on the upper surface; [subfamily Cheilanthoideae].
                 9 Leaves 1-pinnate or 1-pinnate-pinnatifid; lower leaf blade surfaces densely covered with stellate and ciliate-fringed scales; petiole with 2 vascular bundles
                 9 Leaves 1-pinnate-pinnatifid or more divided (to 5-pinnate); lower leaf blade surfaces glabrous to pubescent and/or farinose; petiole with 1 vascular bundle.
                   10 Lower leaf surface with dense white farina.
                     11 Leaf blade deltoid; white farina on lower blade surface not interspersed with shiny, dark-brown needle-like hairs; [of KY westwards]
                     11 Leaf blade lanceolate; white farina on lower blade surface interspersed with shiny, dark-brown needle-like hairs; [of s. TX only in our region]
                   10 Lower leaf surface not farinose, variously glabrous or hairy; [widespread in our region].
                       12 Leaf blade pentagonal in outline, divided into 3-5 segments which are each merely pinnatifid
                          13 Leaves 1-3-pinnate, the ultimate leaf-segments 8-100 mm long, glabrous or sparsely and inconspicuously hairy
                            14 Petioles slightly grooved or flattened and ultimate segments thin in texture and not strongly rolled, and also lacking a mucro or cusp at apex
                            14 Petioles either terete (not grooved/flattened), or petiole flattened, and then the ultimate segments also leathery and strongly rolled and with mucronate apex
                          13 Leaves 2-5-pinnate, the ultimate leaf-segments 1-4 (-8) mm long, more-or-less densely hairy (glabrous or glabrescent in Myriopteris alabamensis and M. microphylla).
                              15 Ultimate leaf segments cordate at the base and well-separated from one another on prominent stalks [of ec. TX only in our region]
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