6. Dryopteris crassirhizoma Nakai (Cat. Sem. Hort. Bot. Univ. Imp. Tokyo 32. 1920).—Fig. 7. 

Rhizome erect, stout, may produce offshoots. Fronds to ca. 150 cm long, 30 cm wide. Stipe short, 1/3?1/5 the length of the blade, fasiculate, densely covered with mid-brown to reddish brown scales, the larger scales thin, glossy, firm membranous, usually reddish brown, linear, lanceolate to ovate, attenuate, to 30 mm long or more; blade mostly oblanceolate, gradually narrowed below, deeply pinnate-pinnatifid next to the rachis in the proximal part of the frond; pinnae linear-lanceolate, basal pair usually more triangular but equilateral, underside of the costa next to the rachis with costal scales tan, triangular, variable, larger ones mostly attenuate, kinky; segments (pinnules) typically closely placed, narrowly oblong, weakly falcate, their apices mostly blunt-rounded, dentately toothed or untoothed, segment side margins mostly weakly crenate, lowest basiscopic segment (pinnule) next to the rachis not free and its side margins subentire. Sori medial, borne on upper part of frond. 

Dryopteris crassirhizoma is a sexual diploid species native to northeastern Asia, where it is abundant. In the past it has been confused with D. filix-mas which differs by having teeth along the side margins of the segments and other characters in the key. This species differs from D. affinis by the characters in the key, and D. crassirhizoma has very thick, glossy stipe base scales, segments long, apex mostly round and untoothed, fronds oblanceolate and green rather than bluish-green in color. When D. pseudo-filix-mas lacks the pinnatifid or pinnate basiscopic pinnule next to the rachis on the lowest pinnae, it may be distinguished from D. crassirhizoma by its truncate to acute pointed more rectangular pinnules with side lobes and acute teeth.

Dryopteris crassirhizoma is semi-deciduous in cool winters and probably deciduous in cold winters. It is easy to grow and is hardy to a January average of 30°F.