Greek kystos, bladder or sac, + pteris, fern, alluding to the indusium shape.

Plants small to medium-sized, epipetric or terrestrial. Rhizomes short-creeping to decumbent. Stipes slender, grooved, straw-colored to medium brown, mostly glabrous, bases with occasional membranous scales; cross sections at bases reveal ends of 2 ribbon-shaped vascular bundles (appearing as linear and parallel lines). Blades 2-pinnate to 2-pinnate-pinnatifid, herbaceous to somewhat coriaceous, glabrous or slightly scaly. Veins free. Sori round to cup-shaped. Indusia hoodlike, attached at bases, free at margins, opening outward, partially overlapping sori.

A genus of about twelve to fifteen species widespread in temperate zones and at higher elevations in the Tropics. Represented in Hawai 'i by two rare, seldom-collected endemic species. There are probably undescribed taxa in the summit region of Mauna Kea and growing on wet, protected ledges and within lava tube entrances in the higher-elevation subalpine zone of Haleakala.

Cystopteris species are quite variable, making them difficult to separate. The two Hawaiian species have been treated as one in the past.

KEY TO THE SPECIES OF CYSTOPTER/S IN HAWAI'I

I. Blades ovate-lanceolate, obtuse-tipped; rachises slightly winged, especially distally; pinnae tips blunt, margins often crenulate, conspicuously and coarsely dentate; pinnules and ultimate segments broad, 2-3 x longer thanwide, close, erect to slightly oblique; pinna stalks 1-2 mm long, slightly winged; sori medial; East Maui, Hawai'i ................... I. C. douglasii

I. Blades linear-triangular, acute-tipped; rachises not winged; pinnae tips acute, margins entire to slightly dentate; pinnules and ultimate segments narrower, 3-6 x longer than wide, well separated, at oblique angle to costae; pinna stalks 2-3.5 mm long, not or minimally winged; sori supramedial to submarginal; Kaua'i, O'ahu, Uina'i, West Maui .......... 2. C. sandwicensis