Endemic

Latin unus, one, + sorus, heap, in reference to the usually single sorus present on the pinnae.

Plants small, terrestrial. Rhizomes erect, narrow, with persistent stipes and rachises. Fronds 8-30 x 0.4-3.0 cm. Stipes very thin, 0.3-0.6 mm diam., purple black to black, shiny, stipe base scales sparse, only at very base, clathrate, opaque except at margins, usually less than 1 mm long, soon deciduous. Blades 1-pinnate, usually long and narrow, dull green, tips ending in gradually reduced pinnae, usually not becoming pinnatifid; rachises purple black to black, shiny. Pinnae 20-35 pairs, 0.2-1.5 x 0.2-0.9 cm, asymmetrical, somewhat elongate-triangular, upper basal margins parallel with rachises, lower margins more or less perpendicular to rachises, margins entire. Veins free except under sori where veins may connect. Sori mostly single, or sometimes a few fused on distal pinna margins.

Diellia unisora, a morphologically variable, federally listed endangered species, is found in scattered locations in mesic forests, usually on steep ridge sides, at about 700 m, in the southern Wai'anae Range of O'ahu. In a few locations it is associated with D. falcata and a hybrid continuum between the two species. (See under Hybrids in this treatment.)

Diellia unisora, a very rare O'ahu spe-cies, may be recognized by its usually small, narrow fronds; usually single sori; dark scales with occluded centers; rhizomes with persistent black, shiny stipes and rachises; and frond tips formed by gradually diminishing, alternate pinnae that usually do not become pinnatifid.