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..
Polypodium Robertianum Hoffm. Deutschl. Fl. 2:
[add. 4]. 1795. Phegopteris Robertiana A. Br.; Aschers. Fl. Brand. 2:
198. 1859. Polypodium calcareum Sm. Fl. Brit. 1117. 1804. Phegopteris calcarea Fee, Gen. Fil. 243. 1850-52.
Rootstock slender, creeping, branched. Stipes slender, straw-colored, 6'-13' long; blades 6'-8' long, s'~7' broad, copiously glandular, suberect, triangular-ovate; basal pinnae largest, 3'-4 1/2' long, unequally deltoid-ovate, long-stalked, 2-pinnatifid; second pair of pinnae distant, short-stalked or sessile, pinnate or 2-pinnatifid, deltoid-oblong; succeeding pinnae sessile, narrower, mostly pinnatifid; segments close, oblong to elongate-oblong, the margins subentire to crenate-dentate, reflexed; sori near the margin, non-indusiate, numerous.
On shaded limestone, Labrador to Alaska. New Brunswick and Iowa. Rare and local Also in Europe.