Formosana refers to the Island of Formosa, now called Taiwan.
Frond: 100 cm high by 35 cm wide, evergreen in warmer areas, monomorphic, blade/stipe ratio: 3:2.
Stipe: grooved, basal scales black-brown, to 1.5 cm, vascular bundles: 3-7 in a c-shaped pattern.
Blade: 3-pinnate at the basiscopic pinnule, less divided upwards, pentagonal, papery, lanceolate or bullate, black scales on the rachis, tan scales on the costae.
Pinnae: 13 to 15 pair, anadromous lowest pinnae pair, opposite; pinnules first basiscopic pinnule of basal pinnae very long, larger pinnules slightly eared; costae grooved above, continuous from rachis to costae; margins serrate, sometimes with two teeth at the end; veins free, forked.
Sori: round, in 1 row between midrib and margin, indusium: reniform, at a sinus, sporangia: brownish.
Habitat: floor of mountain forests.
Distribution: Japan, Taiwan and the Philippines.
Hardy to -20°C, USDA Zone 6.
pentagonal frond and the long basiscopic pinnule
Aspidium formosanum H. Christ
Polystichum constantissimum Hayata
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.