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. 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


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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