After Franz Philipp von Siebold, 19th century German botanist, a specialist in plants of Japan.
Rhizome: short-creeping, scales lanceolate to linear, acuminate at apex, brown to blackish brown, 1--1.2 cm long.
Frond: 50 cm high by 40 cm wide, evergreen, somewhat dimorphic, fertile fronds erect, sterile arching, blade/stipe ratio: 3:1 to 1:2.
Stipe: straw-colored, dark at base, grooved, scaly at base, vascular bundles: 3-7 in a c-shaped pattern.
Blade: 1-pinnate, broadly ovate, papery, hair-like linear scales sparsely persistent on lower surface.
Pinnae: 2 to 6 pair, linear, acuminate, round at base, the sterile pinnae wider, slightly crenate at margins, and a similar terminal pinna, all sessile (or lower pinnae short-stalked); veins free, forked.
Sori: round, dispersed evenly, indusium: reniform, at a sinus, sporangia: brownish.
Habitat: dry floor of mountain forests.
Distribution: Japan and China.
Hardy to -20°C, USDA Zone 6.
the pinnate form is so distinctive that the only confusion would place it as a non-fern
Aspidium sieboldii Van Houtte ex Mett.
Lastrea sieboldii Moore
Nephrodium sieboldii Hook.
Polystichum sieboldii Keys.
Pycnopteris sieboldii Moore
Illustration from The Cultivated Species of the Fern Genus Dryopteris in the United States, Barbara Joe Hoshizaki and Kenneth A. Wilson, American Fern Journal, 89, 1, (1999), with permission.