Etymology Of uncertain derivation: from Latin os, bone + munda, cure, because the root was a remedy for rickets; or perhaps from mundae to clean, as it was used medically to clean bones. Perhaps from Osmunder, the Saxon god of war.

Description Rhizome: erect, massive, forming a trunk, occasionally branching, hairs and old stipe bases woven together with black, fibrous roots.
Frond: deciduous, dimorphic.
Stipe: stipules (flared leaf base), unique to the family/genus, hairy when young, vascular bundles: 1 in a U-shape where the top of the arms continue to curl.
Blade: 1-2-pinnate, rachis grooved, somewhat waxy, shedding water, reddish to light brown hairs.
Pinnae: catadromous, often jointed at the rachis, veins free, forked.
Sori: none, indusium: absent, sporangia: large, globose, tan or black when mature, spores green.

Distinctive Characteristics The winged stipes, the vascular bundle, and the large naked sporangium without sorus or indusium, are all unique characters.