Nephrodium hudsonianum Brack.; Aspidium hudsonianum (Brack.) H. Mann; Cyclosorus hudsonianus (Brack.) Ching; Dryopteris hudsonianum (Brack.) Rosenst.; D. truncata (Gaudich.) Kuntze; Nephrodium truncatum (Gaudich.) C. Presl; Polystichum truncatum Gaudich.; Thelypteris hudsoniana (Brack.) C. F. Reed

Common names: laukahi

Endemic             

Name honors Navy Capt. William Leverreth Hudson (1794-1862), commander of the Peacock, one of the vessels of the U.S. Exploring Expedition ( 1838-I842).

Plants medium-sized to large, terrestrial. Rhizomes decumbent to erect. Fronds to 145 cm long. Stipes grooved, ridges clothed with sharp-tipped hairs, scales only at very base, sparse, brown, soon deciduous. Blades 1-pinnate-pinnatifid, membranous to chartaceous; rachises with 2-4 rounded adaxial ridges with grooves between them, with abundant, short, white, sharp-tipped hairs ad-axially. Pinnae short-stalked to adnate, lanceolate, deeply lobed, cut about 1/2-2/3 of distance to costae, middle pinnae to 25 cm long, acuminate, basal 2-6 pairs abruptly and markedly smaller than next distal pinnae, smallest basal pinnae less than 1 cm long and round, sinuses wide with prominent, cartilaginous, sometimes toothed sinus membranes, aerophores prominent on abaxial bases of pinna costae (more prominent on living material), adaxial surfaces with scattered short, thick, pointed hairs between veins and pointing toward margins, similar but shorter hairs sparse on costae and veins, abaxial surfaces mostly glabrous. Ultimate segments rectangular, oblong, margins with white, pointed hairs, tips obtuse, minutely dentate. Veins pinnately divided, 6-8 pairs, unforked, 1 pair of basal veins from adjacent lobes uniting to form excurrent veins extending to sinuses, more distal veins ending at cartilaginous sinus bases or on margins of ultimate segments. Sori medial, 8-12 per lobe. Indusia thin, small, with a few hairs.

Locally common in mesic to wet forests, (20-)155-760 m, all major islands.

Pneumatopteris hudsoniana may be distinguished by its short, ascending rhizomes crowned with a rosette of medium-sized to large 1-pinnate-pinnatifid fronds with deeply lobed pinnae. The lower pinnae are abruptly reduced in size, a unique feature among Hawaiian ferns. (The lower pinnae of Amauropelta globulifera are smaller, more numerous, and more gradually reduced in size.)