Polypodium unisorum Baker; Gymnogramme sadlerioides Underw.; Sadleria squarrosa (Gaudich.) T. Moore var. depauperata Hillebr.

Common names: 'apu 'u

Endemic

Latin, unus, one, + sorus, heap, in reference to the often single sorus on the ultimate segments.

Plants small. Rhizomes pendent to de-cumbent. Fronds drooping, 17-43 em long. Stipes 1-3 mm wide at base, dark brown to purplish black, abundant glandular hairs present, sparsely covered with scales; scales brown to dark reddish brown, linear-attenuate, tips thin, tapering, abundant glandular hairs on margins. Blades 2-pinnate, lanceolate, subcoriaceous, tips obtuse; rachises sparsely scaly throughout. Pinnae 14-24 pairs, 1.9-3.5 cm long, tips obtuse, glandular hairs present. Ultimate segments 3-7 pairs per pinna, shorter than 0.5 cm, round to ovate, tips obtuse, concave abaxially. Veins obscure. Sori 1-2 per segment. Indusia thin, sparse, and interrupted.

Uncommon in its restricted habitat on steep, dark, damp stream walls in wet forest areas, 400-1,520 m, Kaua 'i only.

Sadleria unisora may be distinguished from S. squarrosa by its narrower stipes and rachises sparsely clothed with narrower, darker scales. It is smaller and has round-tipped pinnae, more obtuse seg-ments, and fewer segments per pinna.