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..
Rootstock stout, ascending. Stipes 8'-12' long, covered below with thin pale-brown scales; blade of fertile leaves elongate-oblong or lanceolate, acuminate, slightly narrowed toward the base, firm, bipinnate, or 3-pinnatifid, 1°-2 1/2° long, 3'-5' wide, the sterile ones commonly shorter and less divided; middle and upper pinnae lanceolate with a broad base, acuminate, those below unequally deltoid-lanceolate, the lowest elongate-triangular; pinnules oblong-ovate, constricted at the base, the lower ones nearly sessile, often pinnatifid, those above adnate and slightly decurrent upon the narrowly winged rachis, serrate, the margins spinulose throughout; sori numerous, distinct, medial or nearer the mid-vein; indusia orbicular-reniform, glandular.
Several American writers regard D. Boottii as a natural hybrid between D. cristata and D. intermedia. Other supposed hybrids have recently been described, which have been confused either with D. Boottii or with species of which they were regarded as aberrant forms. The characters of these are such as to support strongly the hybridity hypothesis. They should be sought in localities exceptionally favorable to a mingling of the supposed parent forms. A list of these, including D. Boottii, follows:
Dryopteris Clintoniana X Goldiana Dowell, Bull. Torrey Club 35: 137. 1908.
Dryopteris Goldiana celsa Palmer, Proc. Biol. Soc. Wash. 13: 65. 1899. Dryopteris Clintoniana X intermedia Dowell, Bull. Torrey Club 35: 136. 1908. Dryopteris Clintoniana X marginalis Slosson, Bull. Torrey Club 37: 202. 1910. Dryopteris Clintoniana X spinulosa Benedict, Bull. Torrey Club 36: 45. 1909. Dryopteris cristata X Goldiana Benedict, Bull. Torrey Club 36: 47. 1909. Dryopteris cristata X intermedia Dowell, Bull. Torrey Club 35: 136. 1908.
Aspidium Boottii Tuckerm. Hovey's Mag. 9: 145. 1843.
Dryopteris Boottii Underw. Nat. Ferns, ed. 4, 117. 1893.
Dryopteris cristata X spinulosa intermedia Slosson, Fern Bull. 16: 97. 1908. Dryopteris cristata x marginalis Davenp. Bot. Gaz. 19: 497. 1894, as syn.
Aspidium cristatnm X marginale Davenp. Bot. Gaz. 19: 494. 1894. Dryopteris cristata x spinulosa (Milde) C. Chr. Ind. Fil. 259. 1905.
Aspidium cristatum X spimdosum Milde, Nov. Act. Acad. Leop.-Carol. 26: 533. 1856. Dryopteris Goldiana X intermedia Dowell, Bull. Torrey Club 35: 138. 1908. Dryopteris Goldiana X marginalis Dowell, Bull. Torrey Club 35: 139. 1908. Dryopteris Goldiana X spinulosa Benedict, Bull. Torrey Club 36: 47. 1909. Dryopteris intermedia X marginalis Benedict, Bull. Torrey Club 36: 48. 1909. Dryopteris marginalis X spinulosa Slosson, Fern Bull. 16: 99. 1908.
Dryopteris pittsfordensis Slosson, Rhodora 6: 75. 1904.
Nephrodium pittsfordense Davenp. Rhodora 6: 76. 1904, as syn.
Aspidium spinulosum X marginale Eggleston, Rhodora 6: 138. 1904.