Asplenium arnottii (Brack.) Baker; A. brevisorum sensu Hook. & Baker, non Wall.; A. diplaziodes Hook. & Am.; Athyrium arnottii (Brack.) Milde; At. gaudichaudii Fee; Diplazium meyenianum sensu auct., non C. Presl [Hillebrand's Asplenium arnottii (Brack.) Baker ~, y, and o vars.]

Common names: ho'i'o, pohole (Maui name)

Endemic

Name honors George A. W. Amott (1799-1868), distinguished Scottish botanist who described many Hawaiian fern species with W. J. Hooker.

Plants medium-sized to large, terrestrial. Rhizomes decumbent, forking, 2.5-5 cm diam. Fronds to 1.2 m long. Stipes straw-colored to pale brown, sparsely scaly at bases, scales thin, lanceolate, pale brown, deciduous. Blades 2-pinnate-pinnatifid to 2-pinnate-pinnatisect, deltate-ovate to deltate-elongate, dark green, thick-chartaceous, glabrous. Pinnae 9-11 pairs, stalked, alternate. Pinnules usually well separated, linear-deltate. Ultimate segments short-stalked proximally, sessile distally, 6-8 mm wide, margins mainly entire, tips rectangular, obtuse, usually dentate. Veins free, prominent. Sori plentiful on all pinnae of fertile fronds, 3-6+ mm long, sometimes extending from mid veins to near margins, some sori doubled near bases of pinnae. Indusia narrow.

Frequent in mesic to wet forests and along stream banks, 150-1,700 m, all major islands. Much less common than Diplazium sandwichianum, with which it hybridizes (see under Hybrids later in this treatment). The description just given is for one extreme of a continuum between D. arnottii and D. sandwichianum. Plants intermediate in character are common, and the full nature of the species and their intermediates needs further study and definition.

Diplazium arnottii is a usually large and 2-pinnate-pinnatifid, colony-forming fern of wet, shady environments that differs from D. sandwichianum by having much longer sori, usually less dissection, a thicker texture, and wider ultimate segments.