Seldom seen but locally common in its restricted habitat under dark, moist, overhanging banks or vegetation, near streambeds.
Plants small to medium-sized; rhizomes decumbent, short with several persistent dead stipes, and 7-20 fronds clustered at tips.
Fronds 10-25 cm long, arranged in a flattened rosette; stipe usually 1/3-1/4 frond length, deeply grooved adaxially, dark brown to black; blade 1-pinnate at base, pinnatifid distally, lanceolate; rachises deeply grooved. Pinnae, usually only basal 1-2 pairs short-stalked; ultimate segment slightly falcate, margin toothed.
Sori short, 1-2 mm long, parallel and close to or touching midrib, almost always in 1 row, very close and often overlapping, elongate; indusia large, often overlapping, with scattered fine hairs.
Name honors Harold Lloyd Lyon (1879-1957), American botanist at Hawaiian Sugar Planters' Association; later a director of Foster Botanical Garden and Manoa Arboretum.