Endemic

O'ahu, + Latin suffix -ensis, indicating place or country of growth or origin.

Plants small, epiphytic. Rhizomes short, erect. Fronds erect to arching 2-10 x 0.2-0.4 cm. Stipes round, short, or nearly absent, be-coming winged and merging with blades. Blades linear, simple, entire, coriaceous, margins occasionally undulate, occasionally slightly crenate if more than 5 cm long, hairs absent, or occasionally present as glandular or eglandular hairs. Veins simple or 1-forked on larger blades. Sori arranged regularly and alternately, usually on upper 1/2-3/4 of frond, glandular paraphyses absent or sparse, on most plants consisting of thin, uniseriate hairs lacking glands at tips.

Locally common epiphyte, especially near streams in deeper parts of valleys, in wet forests, 300-550 m, near the summit of the Ko'olau Range of O'ahu. It grows as an epiphyte on a variety of native trees as well as on guava (Psidium cattleianum), but is seldom found on 'ohi'a (Metrosideros polymorpha). It is often associated with Adenophorus pinnatifidus, with which it hybridizes in scattered locations (see under hybrids).

Adenophorus oahuensis may be easily recognized by its small, narrow, linear, simple fronds clustered on the tips of small rhizomes. It is an epiphyte found mostly near the summit ridge and along streams near the summit of the Ko'olau Range on O'ahu.