Roots not proliferous. Stems erect or ascending, rarely branched; scales black throughout, linear-lanceolate, 2--3 × 0.2--0.4 mm, margin entire, apex attenuate. Leaves monomorphic. Petiole black or purplish black throughout, lustrous, 0.3--5 cm, 1/4--1/15 length of blade; indument of black filiform scales at base. Blade linear or narrowly oblanceolate, 1-pinnate throughout, 6--22(--37) × 1--1.8(--2.3) cm, thin, glabrous; base tapered; apex acute, not rooting. Rachis black throughout, lustrous, glabrous. Pinnae in 15--40 pairs, oblong; medial pinnae somewhat asymmetric, oblong, 4--10 × 2--4(--5) mm; base acute, acroscopically enlarged; margins serrate to crenate, lobed; apex obtuse. Veins free, evident. Sori 3--6 pairs per pinna, on both basiscopic and acroscopic sides of pinnae. Spores 64 per sporangium. 2 n = 144, 216.

Sinkholes, limestone rocks in shady hammocks, masonry; 0--50 m; Fla., Ga.; Mexico; West Indies in Cuba, Puerto Rico; Bermuda; Central America in Belize.

The tetraploid cytotype (4 x ) of Asplenium heterochroum hybridizes with A . resiliens (3 x ) to produce A . × heteroresiliens (5 x ). It is extremely rare and local, known in northern peninsular Florida from Alachua, Citrus, Columbia, Jackson, and Marion counties.