Etymology Formosana refers to the Island of Formosa, now called Taiwan.

Description Rhizome: erect.
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.

Culture Habitat: floor of mountain forests. Distribution: Japan, Taiwan and the Philippines. Hardy to -20°C, USDA Zone 6.

Distinctive Characteristics pentagonal frond and the long basiscopic pinnule

Synonyms
Aspidium formosanum H. Christ
Polystichum constantissimum Hayata