Dennstaedtiaceae
Submarginal or marginal sori; indument usually of hairs rather than scales; and long-creeping stems with stem buds on the bases of the petioles. Here 2 genera.

Dennstaedtia Bernhardi

Cup fern

Etymology Named for the German botanist, August Wilhelm Dennstaedt (1776-1826).
Description Rhizome: long-creeping, hairs dark reddish brown, jointed.
Frond: deciduous, monomorphic.
Stipe: straw-colored to brown, darker at base, grooved above, pubescent with soft, jointed hairs, vascular bundles: 1 arranged in a U-shape.
Blade: 2-pinnate-pinnatifid, less and more also, lanceolate, lacy, papery, yellow-green to pale green, indument of silver-gray, jointed hairs on both surfaces, gland tipped hairs below.
Pinnae: broadest at the base, segments ovate to lanceolate, margins serrate-crenate, veins free, pinnately branched.
Sori: globose to almost cylindric, marginal at vein tips, indusium: formed by fusion of inner and outer laminar flaps to form a circular cup.
Dennstaedtia
Dennstaedtia. Sori here are less than 2 mm, with cup-like indusia constructed partly from the margin, partly from the lamina.  Photo by Rod Tulloss, © Environmental Commission of the Borough of Roosevelt and the Fund for Roosevelt, Inc.

Pteridium Gleditsch ex Scopoli

Bracken

Etymology Greek: pteron, a wing, from the shape of the pinnae, but the ancient Greeks used pteris for ferns in general. The word progresses to pteridion, a small fern.
Description Rhizome: long-creeping, jointed hairs.
Frond: deciduous, monomorphic.
Stipe: pale green, glabrous above with soft hairs at the brown base, vascular bundles: numerous, U- or O-shaped in cross section.
Blade: 2-4 pinnate, broadly deltate, large, papery to leathery.
Pinnae: lowest very large, costae rachis and costae grooved above, veins free, forked, except for a marginal strand.
Sori: continuous, along the margin, indusium: double, the outer false, reflexed, the inner distinct or absent.

Pteridium aquilinum. Hairs, venation, false indusium.  BioImages: The Virtual Field-Guide (UK), photo © Malcolm Storey.

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