Greek athyros, doorless, possibly because in some species the indusium opens slowly and
tardily.

Plants medium-sized, terrestrial. Rhizomes decumbent to erect. Fronds clustered at apex of
rhizomes. Stipes with adaxial groove, usually V-shaped in cross section, cross sections at
bases reveal ends of 2 ribbon-shaped vascular bundles (appearing as linear and parallel
lines). Blades 3- to 4-pinnate, triangular, herbaceous, spinelike appendages often present
on adaxial side at bases of costae and costules; rachises grooved, grooves continuous with
pinnae rachises, and costules. Sari linear or J-shaped. Indusia present.

A genus of about 180 species distributed worldwide. Represented in Hawai 'i by a single
endemic species.