Endemic

Latin insularis, of islands, alluding to its distribution on islands.

Plants medium-sized to large, terrestrial. Fronds 0.3-1.3 m long, usually pendent. Stipes long, around 1/2 the frond length, straw-colored, glossy, bases scaly with large, ovate-lanceolate, long-acuminate, light reddish brown scales, plentiful at base, becoming sparse distally. Blades 3-to 4(-5)-pinnate, triangular-ovate, gradually acuminate, leathery, green to dark green; rachises and costae bearing few scattered, narrow fibrils. Pinnae lanceolate, acute-tipped, tips often upswept, pointing toward frond apex. Ultimate segments elongate-deltate, outward-pointing margins more prominently lobed, lobe tips acuminate to aristate, aeroscopic basal segments closer to costae longer than basiscopic ones. Veins conspicuous, free. Sori round, medial to submarginal on ultimate segments.

Occasionally locally common, often on the sides of periodic stream courses in mid-elevation wet forests, 765-2,015 m, all major islands except Lana'i. Very rare on O'ahu and apparently absent from most of Hawai'i Island, where it is found only along streams near the Kohala Mountains.

Arachniodes insularis was only recently recognized as a distinct endemic species. Previously the species was thought to be native but not endemic to Hawai 'i, and several names were applied to it in various publications and checklists, now all considered misapplied.

Arachniodes insularis may be recognized by the large, pale reddish brown scales at the bases of the frond stalks; ovate-triangular fronds up to well over 1 m long; and finely dissected, 3-to 4(-5)-pinnate fronds with segments and lobes gradually reduced to pointed tips.