Brittle maidenhair fern Latin tener, soft, delicate, + suffix -urn, resemblance or possession, alluding to the frond character.

Plants large, terrestrial. Rhizomes short-creeping, scaly. Fronds clustered, erect to arching, 30-100 cm long. Stipes dark purple brown, shiny, glabrous. Blades 3-to 5-pinnate, deltate to ovate. Ultimate segments vari-able in shape, broadly triangular to diamond-shaped or rhomboidal, fertile segments 1-2 x 1-3 cm, sterile segments smaller, mem-branous, jointed, ultimate segment stalks usually asymmetrically attached, enlarged into saucerlike disks at attachment, black color of the stalks ending abruptly at these disks, sterile outer margins lobed or cleft, toothed. Veins ending in marginal teeth. Sari 8-13 per segment, 1-2 on a lobe, oblong. Indusial flap oblong.

Native to the West Indies, tropical America, and Florida, Adiantum tenerum was first collected in Hawai 'i near the shore of Hana Bay on Maui in 1987 and has since been found naturalized on a rock wall in Makiki on O'ahu. It is probably already more wide-spread but unrecognized or unreported.

Currently known from Hiina on Maui and Makiki in Honolulu, Adiantum tenerum is recognizable by its black pinna and pinnule stalks ending abruptly in black, saucerlike disks, and ultimate segments various shaped and attached asymmetrically to their stalks.