Trichomanes is the ancient Greek name for this fern, meaning "hair of the head", probably from tricho, hairy + manes, flowing.
Rhizome: short-creeping, often branched, scales clathrate, black, or sometimes with brown borders, to 5 mm , lanceolate.
Frond: 20 cm high by 1.5 cm wide, evergreen, monomorphic or nearly so, but the sterile fronds are earlier and prostrate, blade/stipe ratio: 3:1 to 5:1.
Stipe: a diagnostic feature (10x hand lens) is a narrow wing running the length of the stipe and rachis; brown-black or coppery, lustrous all the way to the end of the rachis , dark brown to black, filiform scales at base, then glabrous above, vascular bundles: 2 c-shaped, back to back, uniting to 1 upwards in an x-shape.
Blade: 1-pinnate, linear, widest above the middle, tapering to either end, thin, glabrous or minutely hairy.
Pinnae: 20 to 35 pair, opposite to subopposite, oblong, round at apex; margins finely dentate; veins free, evident.
Sori: oblong to linear, about 1.5 mm long, , 2--5 pairs per pinna, indusium: translucent, pale tan, hidden by sporangia at maturity, on one side of the sorus, sporangia: brown, maturity: late summer to early fall.
Habitat: associated with rocks, and see comments under subtaxa.
Distribution: World, appears here and there on every continent except Antarctica.
Hardy to -35°C, USDA Zone 3.
Young plants may be difficult to distinguish from A. platyneuron, but the latter's pinnae are eared upwards.