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Key to Didymoglossum

Hymenophyllaceae

Didymoglossum

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1 Leaves 1-2× pinnately compound or lobed, with distinctly pinnate venation
1 Leaves entire to irregularly and palmately lobed, with palmate to slightly pinnate venation.
  2 Leaf margins fringed with paired disclike scales; soral involucres 5-15 per leaf; leaf blades 2 cells thick between the veins
  2 Leaf margins fringed with dark stellate hairs; soral involucres 1-6 per leaf; leaf blades 1 cell thick between the veins.
    3 Midvein extending to the apex of the leaf blade; involucral lips not distinct from the blade in color; leaves usually < 1 cm long; soral involucres usually 1 per leaf; [widespread in our area]
    3 Midvein absent or not extending past the midpoint of the leaf blade; involucral lips dark-margined; soral involucres 1-6 per leaf; [of FL peninsula].
      4 Leaves 1-3 cm long; soral involucres not flaring at mouth

Key to Hymenophyllaceae

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1 Gametophytes only present, not in association with or in close proximity to filmy-fern sporophytes.
  2 Gametophytes thalloid, ribbonlike, flattened
  2 Gametophytes filamentous in part or in whole, forming felt-like mats.
    3 Gametophytes strictly filamentous; [of inland physiographic provinces, on ceilings and back walls of rock grottos]
    3 Gametophytes filamentous and also bearing flattened blades tipped by gemmae; [of rotting wood in the Coastal Plain]
1 Sporophytes present.
      4 Leaves simple to slightly lobed, < 2 cm long; rhizomes filiform, <0.5 mm in diameter.
        5 Leaves glabrous or with simple hairs; rhizomes densely covered with dark-colored hairs
      4 Leaves pinnatifid to pinnate-pinnatifid, > 2.5 cm long; rhizomes filiform or moderately stout.
          6 Rhizomes erect, the leaves clustered at the tip; leaves 1-pinnatifid; [of rotting wood in the Coastal Plain]
          6 Rhizomes long-creeping, the leaves scattered along the rhizome; leaves 1-pinnatifid to 1-2 pinnate-pinnatifid; [of inland physiographic provinces, of moist rock].
             7 Leaves with dark stellate hairs in the lobe sinuses; [of Coastal Plain of s. FL]
             7 Leaves lacking stellate hairs; [of inland provinces, rarely Coastal Plain of AL and MS].
               8 Rhizomes filiform, < 0.5 mm in diameter, glabrous or with sparse light-colored hairs; indusium ("involucre") bivalvate (deeply divided into 2 flaps); receptacle not exserted from between the deeply bilobed indusium; margins of finest leaf divisions with sharp teeth pointing towards the division apex (at 20× magnification)
               8 Rhizomes moderately stout, 0.8-1.5 mm in diameter, densely clad with dark-colored hairs; indusium ("involucre") tubular or funnelform, sometimes slightly 2-lobed; receptacle long and whiplike, exserted from the mouth of the tubular (slightly bilobed) indusium; margins of finest leaf divisions entire or with obscure crenations (at 20× magnification)