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..
Small mainly alpine or boreal ferns with dimorphous leaves, the stipes greenish or straw-colored, the blades 2-3-pinnate, the fertile exceeding the sterile. Sori borne at or near the ends of the free forking veins, at length confluent. Indusia formed of the altered reflexed margin of the segment. [Greek, alluding to the sori hidden before maturity.]
Four species, the following and 2 of Europe and Asia. Type species: C. acrostichoides R. Br.
Rootstocks stout, clustered, ascending; fertile segments linear.
Rootstocks slender, creeping; fertile segments much broader.
Cryptogramma acrostichoides R. Br. App. Franklin's Journ. 767. 1823.
Rootstock stout, short, chaffy; leaves clustered, the fertile ones surpassing the sterile. Stipes 2'-6' long, chaffy below, those of the sterile leaves slender, greenish and of the fertile stouter and stramineous; blades ovate or ovate-lanceolate, thin, glabrous, 2-3-pinnate, the sterile ones with the ultimate segments and pinnules crowded, ovate, oblong or obovate, obtuse, crenate or incised; fertile blades with segments 3"-6" long, 1" or less wide, the thin margins involute to the midrib at first, at maturity expanded, exposing the sporanges.
Among rocks, Labrador to Alaska, south to Lakes Huron and Superior, in the mountains to Colorado and California. Summer.
Jahrb. 3: 413. 1882.
Rootstock slender, creeping, somewhat scaly. Stipes scattered, 2-5' long, straw-colored or pale brown, slightly chaffy below; blades thin-membranous, ovate or oblong-ovate, 2'-5' long, 1'-2' wide; pinnae few, the lower nearly 2-pinnate, the middle pinnate, the upper simple; segments of sterile blades ovate to obovate, cuneate, crenately lobed, those of the fertile linear-oblong or lanceolate; indusium broad.
On rocks, preferring limestone, Labrador to Alaska, Pennsylvania, Iowa, Wisconsin and Colorado. Also in Asia. Aug.-Sept.