This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Large or small ferns of various habitat, with simple lobed or 1-3-pinnatifid or pinnate mostly uniform leaves, the veins free; scales of the rootstock firm, with thick-walled cells. Sori straight or sometimes slightly curved, oblong to linear, borne on the oblique veins, usually somewhat apart. Indusia invariably present, attached lengthwise along the veins, usually at the inner side. [Ancient Greek name, being a supposed remedy for the spleen.]
Biades pinnatifid, or pinnate only below, the apices long-attenuate.
Stipe and rachis dark purplish brown throughout.
Stipe dark brownish below, green above; rachis green.
Blades 1-3-pinnate, the apices not long-attenuate.
Blades i-pinnate only.
Stipe and rachis blackish, reddish or purplish brown throughout.
Sori short, nearer the margin than the midvein.
Sori longer, medial or nearer the midvein.
Fertile leaves rigidly erect; pinnae more or less auriculate.
Fertile leaves spreading like the sterile; pinnae not auriculate.
Stipe dark only at the base, green above like the rachis.
Blades small, 2's' long, linear.
Blades large, 1°-2 1/2° long, lanceolate to lanceolate-ovate.
Stipe and rachis green throughout.
Stipe dark brownish, at least toward the base.
Stipes dark at the base, greenish above; rachis green.
Blades deltoid-ovate to deltoid-lanceolate.
Stipe and lower rachis (at least) dark chestnut-brown.