Rough maidenhair fern Latin hispidus, hairy, + ulus, a diminutive suffix, alluding to the fine hairiness of the fern.

Plants stiff, erect, terrestrial. Rhizomes erect to decumbent. Fronds clustered at apex of rhizome, 6-40(-52) cm long, young fronds rosy pink. Stipes dark brown, rough, clothed with short dark fibrils and hairs. Blades 2-to 8-pinnate, deltate to ovate, dichotomously branched at 45o angle, each branch in turn repeatedly forking again; rachises hairy and fibrillose. Ultimate segments nearly sessile or with asymmetrically attached short stalks, often overlapping, dirnidiate, segments oblong-rectangular to diamond-shaped, firm, lower margin entire, upper margin dentate when sterile, both surfaces with fine, short, light hairs. Veins mostly ending in marginal teeth. Sori 6-14 per segment, U-shaped in marginal sinuses. Indusial flap with brown hairs.

Native to Asia (India to Africa), Australia, and Pacific islands, Adiantum hispidulum is now common in dry to wet forests, 90-1,250 (-1,825) m, on all the major islands and Kaho'olawe. It is widely cultivated and was first collected in the wild in Hawai 'i on O'ahu in 1928. It is now a common weed in many mesic, open-canopy forest locations, where it sometimes is an invasive groundcover.

Adiantum hispidulum may be easily recognized by fronds that repeatedly fork at 45° angles; stalks clothed with short, dark fibrils and hairs; and pinnules with short, light hairs.